What are POP3, IMAP and SMTP servers? POP3 session example
Post Office Protocol (POP) - protocol for delivering mail to a user from mailbox POP mail server. Many of the concepts, principles, and concepts of the POP protocol look and function similarly to SMTP. The POP commands are almost identical to the SMTP commands, differing in some details. The figure shows the POP client-server model. The POP server sits between the user agent and the mailboxes.
Currently, there are two versions of the POP protocol - POP2 and POP3, which have approximately the same capabilities, but are incompatible with each other. The fact is that POP2 and POP3 different numbers protocol ports. There is no relationship between them, similar to the relationship between SMTP and ESMTP. The POP3 protocol is not an extension or modification of POP2 - it is a completely different protocol. POP2 is defined in RFC 937 (Post Office Protocol-Version 2, Butler, et al, 1985) and POP3 is defined in RFC 1225 (Post Office Protocol-Version 3, Rose, 1991). Next, we briefly consider POP in general and in more detail - POP3. POP3 is designed with the specifics of delivering mail to personal computers in mind and has appropriate operations to do so.
The Purpose of the POP3 Protocol
Previously, mail messages on most networks were delivered directly from one computer to another. And if the user often changed work computers or one computer belonged to several users, there were certain problems. Nowadays, it is common to deliver a message not to the user's computers, but to special mailboxes of the organization's mail server, which works around the clock (turned on).
Description of the POP3 protocol
The design of the POP3 protocol allows the user to contact his mail server and retrieve the mail that has accumulated for him. The user can access the POP server from any Internet access point. At the same time, he must launch a special mail agent (UA) that works according to the POP3 protocol and configure it to work with his mail server. So, at the head of the POP model is a separate personal computer operating exclusively as a mail system client (server). We also emphasize that messages are delivered to the client using the POP protocol, but are still sent using SMTP. That is, there are two separate interface agents to the mail system on the user's computer - delivery (POP) and sending (SMTP). The designers of the POP3 protocol call this situation "split UAs". The concept of separate agents is briefly discussed in the POP3 specification.
The POP3 protocol specifies three stages in the process of receiving mail: authorization, transaction, and update. Once the POP3 server and client have established a connection, the authorization phase begins. During the authorization stage, the client identifies itself to the server. If the authorization is successful, the server opens the client's mailbox and the transaction phase begins. In it, the client either asks the server for information (for example, a list of mail messages) or asks it to perform a certain action (for example, issue a mail message). Finally, at the update stage, the communication session ends. Table 7 lists the POP3 protocol commands that are required for an Internet-based implementation of the minimum configuration.
Table 5. POP protocol version 3 commands (for minimal configuration)
Team
Description
USER Identifies the user with the given name.
PASS
Specifies the password for the client-server pair
QUIT
Closes a TCP connection
STAT
The server returns the number of messages in the mailbox plus the size of the mailbox
LIST
Server returns message IDs along with message sizes (command parameter can be a message ID)
RETR
Retrieves a message from the mailbox (requires a message ID argument)
DELE
Marks a message for deletion (requires a message ID argument)
NOOP
The server returns a positive response but does nothing
LAST
Server returns highest number messages from those previously accessed
RSET
Undoes the deletion of a message previously marked with a DELE command
Several commands are defined in the POP3 protocol, but only two responses are given to them: +OK (positive, similar to an ACK confirmation message) and -ERR (negative, similar to a NAK not acknowledged message). Both responses confirm that the server has been contacted and is responding to commands at all. As a rule, each answer is followed by its meaningful verbal description. RFC 1225 has examples of several typical POP3 sessions. Now we will consider several of them, which will make it possible to catch the sequence of commands in the exchange between the server and the client.
After the program has established a TCP connection to the POP3 protocol port (official number 110), you must send the USER command with the username as a parameter. If the server response is +OK, send a PASS command with that user's password:
CLIENT: USER kcope
ERVER: +OK
CLIENT: PASS secret
SERVER: +OK kcope's maildrop has 2 messages (320 octets)
(There are 2 messages (320 bytes) in the kcope mailbox...)
POP3 transactions
The STAT command returns the number of messages and the number of bytes in the messages:
CLIENT: STAT
SERVER: +OK 2 320
The LIST command (with no parameter) returns a list of messages in the mailbox and their sizes:
CLIENT: LIST
SERVER: +OK 2 messages (320 octets)
SERVER: 1 120
SERVER: 2200
SERVER: . ...
The LIST command with a parameter returns information about the given message:
CLIENT: LIST 2
SERVER: +OK 2 200 ...
CLIENT: LIST 3
SERVER: -ERR no such message, only 2 messages in maildrop
The TOP command returns the header, an empty string, and the first ten lines of the message body:
CLIENT: TOP 10
SERVER: +OK
SERVER:
(the POP server sends the message headers, an empty string, and the first ten lines of the message body)
SERVER: . ...
CLIENT: TOP 100
SERVER: -ERR no such message
The NOOP command does not return any useful information, except for a positive response from the server. However, a positive response means that the server is connected to the client and is waiting for requests:
CLIENT: NOOP
SERVER: +OK
The following examples show how the POP3 server performs actions. For example, the RETR command retrieves the message with the specified number and puts it in the local UA's buffer:
CLIENT: RETR1
SERVER: +OK 120 octets
SERVER:
(POP3 server sends the whole message)
SERVER: . . . . . .
The DELE command marks the message to be deleted:
CLIENT: DELE1
SERVER: +OK message 1 deleted ...
(post 1 deleted)
CLIENT: DELE2
SERVER: -ERR message 2 already deleted
Post 2 has been deleted.
The RSET command removes the deletion marks from all previously marked messages:
CLIENT: RSET
SERVER: +OK maildrop has 2 messages (320 octets)
(2 messages in mailbox (320 bytes))
As expected, the QUIT command closes the connection to the server:
CLIENT: QUIT
SERVER: +OK dewey POP3 server signing off
CLIENT: QUIT
SERVER: +OK dewey POP3 server signing off (maildrop empty)
CLIENT: QUIT
SERVER: +OK dewey POP3 server signing off (2 messages left)
Note that messages marked for deletion are not actually deleted until the QUIT command is issued and the update phase begins. At any time during the session, the client has the option to issue a RSET command and all messages marked for deletion will be restored.
This article covers the most commonly used email protocols on the Internet - POP3, IMAP, and SMTP. Each of them has a specific function and way of working. The content of the article explains which configuration is best suited for the specific needs of the user when using an e-mail client. It also reveals the answer to the question of which protocol supports e-mail e-mail.
What is POP3?
Version 3 Protocol (POP3) is a standard mail protocol used to receive email from a remote server to a local mail client. Allows you to download messages to your local computer and read them even if the user is in offline. Please note that when using the POP3 protocol to connect to your account messages are downloaded locally and deleted from the email server.
By default, the POP3 protocol runs on two ports:
port 110 is an unencrypted POP3 port;
port 995 - this should be used if you want to securely connect to POP3.
What is IMAP?
Internet Message Access Protocol (IMAP) is an email retrieval protocol used to access it on a remote web server from local client. IMAP and POP3 are the two most commonly used protocols for receiving emails and are supported by all modern email clients and web servers.
The POP3 protocol assumes that your email address is accessible only from one application, while IMAP allows you to log in from multiple clients at the same time. That's why IMAP fit better if you are going to access your e-mail from different places or if your posts are managed by multiple users.
The IMAP protocol runs on two ports:
port 143 is the default unencrypted IMAP port;
port 993 - this must be used if you want to securely connect using IMAP.
What is SMTP?
The protocol is the standard protocol for sending email over the Internet.
SMTP works on three ports:
port 25 is unencrypted by default;
port 2525 - this is opened on all SiteGround servers if port 25 is filtered (for example by your ISP) and you want to send unencrypted emails using SMTP;
port 465 - This is used if you want to send messages securely using SMTP.
What protocols are used for e-mail exchange? Concepts and terms
The term "email server" refers to the two servers needed to send and receive emails, i.e. SMTP and POP.
The incoming mail server is the server associated with your email address account. It cannot have more than one incoming mail server. Access to incoming messages requires an email client, a program that can receive email from an account, allowing the user to read, forward, delete, and reply to messages. Depending on your server, you can use a dedicated email client (such as Outlook Express) or a web browser. So, Internet Explorer used to access email-based accounts. Letters are stored on the incoming mail server until they are downloaded. Once you have downloaded your mail from the mail server, you will not be able to do it again. To successfully upload data, you must enter correct settings in electronic mail program. Most incoming mail servers use one of the following protocols: IMAP, POP3, HTTP.
Outgoing mail server (SMTP)
This is the server used only for sending emails (for transferring them from your email client program to the receiver). Most outgoing mail servers use Protocol to send mail. Depending on your network settings The outgoing mail server may belong to your ISP or the server where you set up your account. Alternatively, you can use a subscription based SMTP server which will allow you to send emails from any account. Due to spam issues, most outgoing mail servers won't let you send emails unless you're logged into your network. A server with an open relay will allow you to use it to send emails, whether you belong to its network group or not.
Email Ports
For networks, a port means the endpoint of a logical connection. The port number determines its type. The default email ports are listed below:
POP3 - port 110;
IMAP - port 143;
SMTP - port 25;
HTTP - port 80;
secure SMTP (SSMTP) - port 465;
secure IMAP (IMAP4-SSL) - port 585;
IMAP4 over SSL (IMAPS) - port 993;
Secure POP3 (SSL-POP) - port 995.
Email protocols: IMAP, POP3, SMTP and HTTP
Basically, the protocol is standard method used at each end of the link. To deal with email, you must use a special client to access the mail server. In turn, they can exchange information with each other using completely different protocols.
IMAP protocol
IMAP (Internet Message Access Protocol) is a standard protocol for accessing email from your local server. IMAP is a client/server protocol in which email is received and the data is stored by your Internet server. Because it only requires a small amount of data transfer, it works well even on a slow connection, such as a dial-up connection. When trying to read specific message The email client downloads data from the server. You can also create and manage folders or mailboxes on the server, delete messages.
POP3 protocol
The Post Office Protocol 3 (POP) email transfer protocol provides a simple, standardized way for users to access mailboxes and download messages to their computers.
When using the POP protocol, all your email messages will be downloaded from the mail server to the local computer. You can also leave copies of your emails on the server. The advantage is that once your messages have been downloaded, you can turn off your internet connection and read your e-mail at your leisure without incurring additional communication costs. On the other hand, with this protocol, you receive and download a lot of spam messages(including spam or viruses).
SMTP protocol
Protocol used by the Mail Transfer Agent (MTA) for delivery electronic messages to a specific recipient server. SMTP can only be used to send emails, not to receive them. Depending on your network or ISP settings, you may only use the SMTP protocol under certain conditions.
HTTP protocols
HTTP is not a protocol designed for email communication, but it can be used to access your mailbox. It is also often referred to as web email. It can be used to compose or receive emails from your account. hotmail- good example using HTTP as the email protocol.
Managed File Transfers and Networking Solutions
Your ability to send and receive email is mainly due to three TCP protocols. They are SMTP, IMAP and POP3.
SMTP
Let's start with SMTP because its main function is different from the other two. The SMTP protocol, or Simple Mail Transfer Protocol, is primarily used to send email from an email client (for example, Microsoft Outlook, Thunderbird or Apple Mail) to the email server. It is also used to relay or forward mail messages from one mail server to another. This is necessary if the sender and recipient have different email service providers.
SMTP, which is specified in RFC 5321, uses port 25 by default. It can also use port 587 and port 465. The latter, which was introduced as the port of choice for secure SMTP (a.k.a. SMTPS), is deprecated. But in fact, it is still used by several mail service providers.
POP3
The Post Office Protocol, or POP, is used to retrieve email messages from latest version that is widely used is version 3, hence the term "POP3".
POP version 3, specified in RFC 1939, supports extensions and several authentication mechanisms. Authentication features are required to prevent attackers from gaining access to user messages.
The POP3 client receives the email like this:
connects to the mail server on port 143 (or 993 for SSL/TLS connections);
retrieves email messages;
serves to connect before closing the mail client application and download messages on demand.
connects to the mail server on port 110 (or 995 for SSL connections/TLS);
deletes copies of messages stored on the server;
disconnects from the server.
Although POP clients can be configured so that the server can continue to store copies of downloaded messages, the above steps are common practice.
IMAP
IMAP, especially Current version(IMAP4) is a more complex protocol. This allows users to group related messages and place them in folders, which in turn can be organized hierarchically. It is also equipped with message flags that indicate whether a message has been read, deleted, or received. It even allows users to search server mailboxes.
Operation logic (imap4 settings):
Please note that messages are not deleted on the server. This can have serious consequences. The IMAP specifications can be found in RFC 3501.
Choosing between IMAP and POP3
Since the basic function of SMTP is fundamentally different, the dilemma of choosing the best protocol usually involves only IMAP and POP3.
If storage space on the server is important to you, then choose POP3. A server with limited memory is one of the main factors that can force you to support POP3. Because IMAP leaves messages on the server, it can consume memory space faster than POP3.
If you want to access your mail at any time, then it's better to stick with IMAP. There is one good reason why IMAP was designed to store messages on the server. It is used to search for messages from multiple devices - sometimes even at the same time. So if you have an iPhone, android tablet, laptop and desktop and you want to read email from any or all of these devices, then IMAP is your best bet.
Synchronization is another benefit of IMAP. If you're accessing email messages from multiple devices, you'll likely want them all to show whatever actions you've taken.
For example, if you're reading messages A, B, and C, you want them to be marked as "read" on other devices as well. If you have deleted letters B and C, you will want the same messages to be deleted from your mailbox on all gadgets. All of these synchronizations can only be achieved if you use IMAP.
Because IMAP allows users to organize messages hierarchically and place them in folders, it helps users better organize their correspondence.
Of course, everything functionality IMAPs come with a price. These solutions are harder to implement and end up consuming a lot more CPU and RAM, especially when it's doing the synchronization process. Actually high loading cpu and memory can happen both client side and server side if there are a ton of messages to sync. From this point of view, the POP3 protocol is less expensive, although less functional.
Privacy is also one of the issues that will depend heavily on end users. They would generally prefer to download all email messages and not leave a copy of it on an unknown server.
Speed is an advantage that varies and depends on the situation. POP3 has the ability to download all email messages on connection. And IMAP can, if necessary (for example, when there is not enough traffic), download only message headers or certain parts and leave attachments on the server. Only when the user decides that the remaining parts are worth downloading will they become available to him. Therefore, IMAP can be considered faster.
However, if all messages on the server must be downloaded every time, then POP3 will be much faster.
As you can see, each of the described protocols has its advantages and disadvantages. It's up to you to decide which features or capabilities are more important.
Also, the desired way to access the e-mail client determines the preference of the protocol. Users who only work from one machine and use webmail to access their new emails will appreciate POP3.
However, users who exchange mailboxes or access their emails with different computers, will prefer IMAP.
Spam firewalls with SMTP, IMAP and POP3
Most spam firewalls only deal with and protect the SMTP protocol. The servers send and receive SMTP email and they will be checked by the spam firewall on the gateway. However, some spam firewalls provide the ability to protect POP3 and IMAP4 when external users need these services to access their email.
SMTP firewalls are transparent to end users; there are no configuration changes for clients. Users still receive and send email messages to the email server. For example, Exchange or Dominos must configure proxy-based message routing to the firewall when sending email, and also provide the ability to send email from the firewall.
In this lesson, we will look at another email protocol that mail clients communicate with mail servers.
I don't think you will be installing a local email client. But, it is on the example of a local mail client that it is easier to understand what they are mail protocols and in particular the POP3 protocol.
I want to make a reservation right away that we are considering protocols for receiving (retrieving) e-mail from mail servers IMAP(imap, i-map) and POP3(pop three). But we do not consider (yet) the protocol for transferring e-mail to mail servers SMTP(es-um-tee-pee).
Although there is nothing special about the SMTP protocol, we will briefly touch on it a bit later.
So, setting up email reception using the POP3 protocol.
We will not invent anything new, but we will simply create another account for our test address [email protected].
To do this, launch our email client program, left click on the "name" of our single account " [email protected]”, and then left-click again on the menu item to create an email account.
In the next window, fill in the fields in the same way as we filled in these fields when setting up an account using the IMAP protocol. Then click on the "Continue" button.
In the next window, we are offered a choice of which protocol we will use to “pick up” our mail from the mail server. We left-click first on the “POP3” selection button, and then again with the left mouse button on the “Finish” button.
Thus, we have created another account in the mail client, with the help of which we will connect to the mail server and collect mail using the POP3 protocol.
The Inbox folder is currently empty, as the client checks mail on the server once every 10 minutes. We will not wait 10 minutes and will check the mail on the mail server immediately. To do this, press the button of the menu item "Get".
Here we will begin to consider the principle of mail over the POP3 protocol.
Mail from the mail server is completely "downloaded" to your personal computer. In other words, it is copied to your computer in full.
And, now, you can work with e-mail completely offline. The mail that is on your personal computer, is no longer associated with the mail server, unlike the IMAP protocol.
But before we continue, let's change the name of the email account created to work with the mail server using the POP3 protocol.
The fact is that the program substitutes an email address for the account name. And since we have two accounts for one email address, then we got two identical names for different accounts.
In general, in order not to get confused, we change the name of the “account”.
To do this, hover over the name of our account " [email protected]” and click on it with the left mouse button. Similarly, click on the account settings menu item “View settings for this account”.
This will open the settings window for our accounts. We change the name of our "account". In order not to invent anything, I'll just add "( pop3)».
It's now easier to navigate our accounts.
Let's assume that we have already looked through all the email and we no longer need it. And we decided to delete all letters at once. To do this, left-click on any letter. Using the key combination "Ctrl + A" select all the letters at once and press the "Del" key to delete.
All mail has been deleted and has been moved from the Inbox to the Deleted Items folder.
And now WARNING!!! Two points.
Now, until a new letter arrives, the Inbox folder will be empty. This seems to go without saying. But!
Let's see what really happens with our mail on the mail server, which we deleted from ourselves. Let's look through an account configured for the IMAP protocol and through .
All remote mail remained on the mail server. Although we don't get it anymore. Is it good or bad?
There are more cons than pros here. Although who cares.
One of the "long" disadvantages is that the volume of letters will increase over time and can completely clog the mailbox. Letters will simply stop coming.
One of the "big" pluses is that even if we completely delete our mail on local computer, we will always know that we have, as it were, a “backup copy” of all our letters
Let's now change one parameter on the server.
To do this, we will enter the account settings view.
Left click on the account name [email protected](pop3)", then "View Account Settings", then "Server Settings".
Uncheck the box next to "Leave a copy of messages on the server." We press the "OK" button.
Now let's see what's up with our mail on the mail server in our mailbox.
As we can see, all mail was deleted immediately after we unchecked the "Leave a copy of messages on the server" option.
Is it good or bad?
There is a very big plus here. You don't need to worry about your mailbox on the server. It just never overflows, and letters will always come.
Of the big disadvantages is that if your computer fails, then all mail will simply be lost, unless, of course, backups have been made.
But, on the other hand, if not backup something, then this very “something” can no longer be restored. And it does not matter what it is - mail, photographs, documents, etc.
In principle, in most cases, the account in the mail client to receive mail from the mail server is configured exactly according to the POP3 protocol, without leaving mail in the mailbox on the server.
But of course, no one ever creates two accounts for the same email address. Although, as you can see, such a possibility exists. And I made two entries just for a visual example.
That's basically all about the IMAP and POP3 protocols.
In the next lesson, we will learn how to "link" email, working with a mailbox through the Web interface. Let's also look at a few various ways insert pictures. 
In conclusion, I want to congratulate all my readers on the upcoming new year and wish everyone health, success and happiness in their personal lives.
That's all for today. Good luck and creative success to all. 🙂
Chances are, most of you reading this guide are already familiar with the most commonly used communication technology, email. But have you ever wondered how it actually works? In this article, we will learn how this service works and what is POP3, SMTP and IMAP.
POP3(Post Office protocol version 3) is often used to communicate with a remote email server and download messages to a local email client and then delete it on the server, e.g. Thunderbird, Windows Mail, etc. However, usually email clients offer a choice - whether or not to leave copies of messages on the server. If you use multiple devices to send messages, then it is recommended to leave this feature enabled, otherwise, on another device you will not have access to sent messages that have not been saved on a remote server. It's also worth noting that POP3 is a one-way protocol, which means that data is taken from a remote server and sent to a local client.
The default POP3 ports are:
Port 110 - non-encrypted port
Port 995 is the SSL/TLS port, also known as POP3S
Step 2 - Differences between POP3 and IMAP, and what ports does IMAP have?
IMAP (protocol application layer to access e-mail), as well as POP3 is used to receive e-mail messages on a local client, however, it has a significant difference - only the headers of e-mail messages are downloaded, the body of the letter itself remains on the server. This protocol communication works in two directions, if changes occur on the local client, they are transmitted to the server. IN Lately IMAP has become more popular as email giants like Gmail recommend using it instead of POP3.
The default IMAP ports are:
- Port 143 - non-encrypted port
- Port 993 is the SSL/TLS port, also known as IMAPS
Step 3 - SMTP, the protocol for outgoing email communication
Simple Mail Transfer Protocol ( SMTP) is used to communicate with a remote server and then send messages from the local client to the remote server, and ultimately to the recipient's server. On your email server, this process is controlled by a special service ( MTA). It is worth mentioning that SMTP is used exclusively for sending messages.
SMTP Ports:
- Port 25 - non-encrypted port
- Port 465 is the SSL/TLS port, also known as SMTPS
Conclusion
We hope that you now have a clear understanding of how mail protocols work and what ports they use. In this guide, we learned what POP3, SMTP and IMAP are and what they are used for. For example, POP3 and IMAP are used for the same purposes, but they approach these tasks in different ways. IMAP leaves the contents of the email on the server, while POP3 downloads it to your computer. Also, we learned what standard ports SMTP, POP3 and IMAP.
Published on 11/17/2017 00:48POP3 (Post Office Protocol) is a protocol, an application layer standard, used by local email clients to receive data from a remote server over TCP/IP connections.
POP3 is used to communicate remotely with an email server and download mail with a local email client. If you are accessing the same account with various devices, we recommend that you keep the deleted copy items, because otherwise, the second device to download the e-mail if the first one is already deleted. It should also be noted that POP3 is a one-way communication protocol, which means that data is taken from a remote server and sent to the local client.
POP3 Port: Technology Overview
The POP protocol supports requests, downloads and deletes, to access mailboxes (so-called maildrop POP-RFCs). The good thing is that most clients have the ability to leave mail on the server after downloading, the email application using POP, connects, typically receives all emails, saves them on the user's COMPUTER as new messages, deletes them from the server, and then disconnects.
Other protocols such as IMAP (Internet Message Access Protocol) to provide a more complete and sophisticated remote access to the types of mailbox operations. In the late 1990s and early 2000s, fewer than a number of ISPs supported IMAP because of the storage space that was needed on the service provider's equipment.
Modern e-mail clients support POP. Over time, popular Postal office software, IMAP support added.Specifications
The server is running on the well-known port 110. POP3 SSL port of the latest standard general use. An encrypted connection for the protocol is offered using STLS or POP3S commands) that connects to the server using transport layer security (TLS) or secure sockets layer (SSL).
Available client messages are captured when the POP3 server port opens the mailbox and valid number messages, the location for this session is a unique identifier assigned to the message. This parameter is persistent and unique to maildrop and allows the client to access the position in different sessions. Messages marked for deletion by message number. When the client disconnects from the session, the mail then deletes the maildrop to delete.
History and documentation
The first version (POP1) was defined in RFC 918 (1984), POP2 RFC 937 (1985). POP3 was initiated by RFC 1081 (1988). RFC 1939 are updated with the RFC 2449 extension mechanism and the authentication mechanism in RFC-1734.
POP3 currently supports multiple authentication methods to ensure various levels protection against unauthorized access to the user's e-mail. Most of these are provided through the POP3 extension mechanisms. Clients support SASL authentication methods with the AUTH extension. The Athena project from MIT has also released a version of Kerberized. RFC 1460 introduced APOP to the protocol. APOP is a challenge/response protocol that uses MD5 hash functions to avoid repeated privacy attempts.
POP4 exists only as an unofficial proposal, adds a record keeping base, support for multiple messages, and a message indicator control in competition with IMAP. The POP4 version has not been developed since 2003. Extensions and specifications
A mechanism was proposed in RFC 2449 to accommodate common extensions, but also organized support for commands such as TOP and UIDL. The RFC does not intend to encourage expansion and has confirmed that POP3's role is to provide simple support, mainly for downloading and deleting mailbox processing requirements.
The extension in the official documentation is called capabilities and the CAPA command list. With the exception of APOP, optional commands that have been included in the feature set. STARTTLS and SDPS extension
This extension allows you to use the Transport Layer Security protocol and Secure Sockets Layer using the STLS command on the POP3 port and not on the other. Some clients and servers use a different port method that uses TCP port 995 (POP3S).
Demon on the Internet introduced an extension for POP3 that allows you to combine multiple accounts on the same domain, and became known as the Disabled POP3 Service (SDPS). To access each account includes a hostname like john@hostname or john+hostname.
Kerberized Post Office Protocol
When calculating, email clients can use the Kerberized Post Office Protocol (KPOP) Internet protocol to receive email from a remote server over a TCP/IP connection. The KPOP protocol is based on the POP3 protocol with the difference that it adds to the Kerberos security and runs on the default port number TCP-1109 instead of 110. Server software version, on the Cyrus IMAP server. Comparison with IMAP
The POP3 SSL port is much simpler than the protocol which makes it easier to implement. Mail moves messages from the email server to the local computer, although it is usually possible to leave the messages on the email server.
IMAP by default, leaves a message on mail server by simply downloading a local copy of it.
POP manages the mailbox like a single store and has no idea on the folders.
The IMAP client performs complex queries, asking the server for the headers or content of certain messages, or looking for emails that match certain criteria. Messages in a deposit dialog can be marked with various status flags (such as "deleted" or "replied"), and they remain in the store until the user explicitly deletes them.
IMAP is designed to treat mailboxes as if they were local. Depending on the client's implementation of the IMAP architecture and system requirements, the manager, the user may write messages directly to the client machine, or save them on the server, or they may choose to.
The POP protocol requires that the currently connected client has only one client connected to the mailbox. Conversely, the IMAP protocol allows simultaneous access by multiple clients and provides mechanisms for detecting mailbox changes by other, simultaneously connected clients.
When POP receives a message, it receives all of its parts, while the IMAP4 protocol allows clients to receive MIME parts separately - for example, to receive text without attachments.
IMAP maintains flags on the server to keep track of the status of a message: for example, if the message is read, if the reply is deleted, if the email.
What is POP and IMAP and what should be used for email?
If you already have an email client or application installed, you will encounter the POP3, SMTP, and IMAP ports conditions. Do you remember which one you chose and why? If you're not entirely sure what these terms and conditions mean, and how each affects your e-mail account, the information below will shed some light on this. This article explains how POP and IMAP protocols work and will help you decide which one best suits your needs.
Both messaging protocols allow you to read email messages locally using third party application. Examples of this are Outlook, Thunderbird, Eudora, libpng-dev, or (Mac) Mail.
Source POP protocol. It was created in 1984 as a tool to download email from a remote server. IMAP was developed in 1986 to provide remote access to email stored on a remote server. In fact, the main difference between the two protocols is that POP downloads emails from the server to permanently store the data locally, while IMAP leaves them on the server and just caches (temporarily stored) emails in place. In other words, IMAP is a form of cloud storage.
Distinguishing features of POP and IMAP?
These two protocols are best compared considering the basic workflows.
POP work process: connecting to the server; receiving e-mail; storing data locally; deleting correspondence from the server; disconnecting.
The default POP behavior is to delete messages from the server. However, most clients also provide the option to leave a copy of downloaded mail on the server.
Default POP3 ports: port 110 - port; port 995 - SSL / TLS port, also known as POP3S.
IMAP workflow: connecting to the server; displaying user-requested content and local caching (list of new messages, message summaries and message content); handling user modifications, such as marking messages as read, deleting data; shutdowns.
As you can see, the IMAP process is a bit more complex than POP. Indeed, the folder structure and e-mail messages are stored on the server, and a copy is made locally. Typically, these local copies are stored temporarily. However, available for storage on a permanent basis.
Default IMAP ports: port 143 - port; port 993 - SSL / TLS port, also known as IMAPS. What are the benefits of POP music?
Being POP in origin, the idea that only the client requires access to email on the server should be simplified, and that letters are better stored locally. This results in the following benefits: Email is stored locally, meaning it is always available, even without an internet connection Internet connection is only needed to send and receive email Saves space on the server Ability to leave a copy of messages on the server Consolidation of multiple accounts e-mail and mailbox servers. What are the benefits of IMAP?
As mentioned in the introduction, IMAP was created to provide remote access to email stored on a remote server. The idea was to allow multiple clients or users to manage even a mailbox. Thus, regardless of the device with which you log into your account, you will always be able to see the same structures, email and folders, as they are stored on the server, and all changes made to the local copy are immediately synchronized with server.
As a result, IMAP has the following advantages: mail stored on a remote server, accessible from multiple locations; to access your email, you must be connected to the Internet; more quick overview, for headers only, until the content is explicitly requested; mail is automatically reserved if the server is managed properly; local storage is registered; the ability to store mail locally. What is an email protocol?
The choice of protocol depends on your specific needs and current working situation. The following points should help you make your final decision.
Choose POP if: You want to access your e-mail from one device. You need constant access to your e-mail, regardless of the presence of the Internet. You have limited storage on the server.
Choose IMAP if: You want to access your email from multiple devices. You have a reliable and constant Internet connection. You want to get a preview of new messages or messages on the server. Your storage space is limited. .
If in doubt, please refer to IMAP. This is a newer protocol that allows you to be flexible and your e-mail will be automatically reserved on the server. Also, server space is usually not an issue these days and you will always be able to store important emails locally. Mail client bugs
If you notice an error, POP3, port: 995, security (SSL) number 0x800C0133, when you try to check your Gmail, then try compressing your mail folders. In the POP client, choose File > File > Compress All Folders. This should fix the problem.