Mail protocols POP3 and IMAP. What are POP3, IMAP and SMTP servers

In this lesson we will look at another email protocol, through which email clients “communicate” with mail servers.

I don't think you will install a local email client. But, using the example of a local mail client, it is easier to understand what mail protocols are and, in particular, the POP3 protocol.

I would like to make a reservation right away that we are considering protocols for receiving (retrieving) email from mail servers IMAP(imap, i-map) and POP3(pop three). But we are not considering (yet) the protocol for transmitting email to mail servers SMTP(es-um-tee-pee).

Although there is nothing special about the SMTP protocol, we will briefly touch on it a little later.

So, setting up email reception using the POP3 protocol.

We won’t invent anything new, we’ll just create one more account for our test address [email protected].

To do this, launch our email client program, left-click on the “name” of our only account “ [email protected]", and then again left-click on the menu item for creating 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 which we will connect to the mail server and receive mail via the POP3 protocol.

The “Inbox” folder is still empty, since 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, click the “Get” menu item button.

This is where we will begin to look at how POP3 mail works.

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 email completely autonomously. The mail that is on your personal computer is now in no way connected 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 POP3 mail server.

The fact is that the program substitutes an email address for the account name. And since we have two accounts for one email address, we ended up with 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 the mouse 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)».

Our accounts are now easier to navigate.

Let's assume that we have already looked through all the email and we no longer need it. And we decided to delete all the letters at once. To do this, left-click on any letter. Use the key combination “Ctrl+A” to select all letters at once and press the “Del” key to delete.

All mail was deleted and moved from the Inbox to the Deleted Items folder.

And now ATTENTION!!! 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's really going on 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 deleted mail remained on the mail server. Although we don't get it anymore. Is it good or bad?

There are rather more minuses than pluses here. Although it depends on who.

One of the “long” disadvantages is that the volume of letters will increase over time and can completely clog the mailbox. The letters will simply stop coming.

One of the “big” advantages is that even if we completely delete our mail on the local computer, we will always know that we have a kind of “backup copy” of all our letters

Let's now change one parameter on the server.

To do this, let's go to view account settings.

Left-click on the account name “ [email protected](pop3)”, then click on “View account settings”, then click on “Server settings”.

Uncheck the box next to “Leave copies of messages on the server.” Click the “OK” button.

Now let's see what's happening with our mail on the mail server in our mailbox.

As we can see, all mail was deleted immediately after we unchecked the “Leave copies 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 will simply never overflow, and letters will always come.

The big disadvantage is that if your computer fails, then all your mail will simply be lost, unless, of course, you made backup copies.

But, on the other hand, if there is no backup copy of something, then this “something” cannot be restored. And it doesn’t matter what it is - mail, photographs, documents, etc.

In principle, in most cases, an account in a mail client to receive mail from a mail server is configured using the POP3 protocol, without leaving mail in a 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 illustrative purposes.

That's basically all about the IMAP and POP3 protocols.

In the next lesson we will learn how to “bind” email by working with a mailbox through the Web interface. We’ll also look at several different ways to 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 everyone. 🙂

POP3

POP3 is a protocol for receiving email messages.

When viewing mail using the POP3 protocol, all emails are downloaded to the user's computer and automatically deleted from the server (although this can be disabled). All further actions with letters will be performed on the user’s computer.

The POP3 protocol is preferable if only one person from a single computer uses the mailbox, and access to mail is necessary even if there is no Internet connection.

IMAP

IMAP is a protocol that supports receiving and managing email directly on the mail server.

When using the IMAP protocol, emails are always on the server and are downloaded from there every time they are viewed. This is very convenient when several people need to have access to the mailbox - all operations with letters that one of them performs (changing the status of a letter to “read”, moving letters between folders, etc.) will be seen by everyone else. The disadvantage is that to work with mail, even with old letters, you need an active Internet connection.

SMTP

An SMTP server is a mail server that only supports sending email.

When using an SMTP server, port 25 is used. Some ISPs block port 25. In this case, you will need to either contact your network administrator to unblock the port, or use the alternative port 587.

Currently, there are a lot of methods of communication via the Internet. You can use ICQ or Skype, social networks, and other resources. About two decades ago, the only way to send or receive virtual mail was through email.

Until a certain time, servers processing user letters had limited capabilities. Storing large amounts of information was expensive, which meant deleting the message from the disk as soon as it was downloaded to the client's computer. Progress has moved forward, there are more opportunities, the user can store letters in a mailbox on a central server for an unlimited amount of time, and carry out various operations with them.

Data transfer protocols used when working with email

Any form of communication has a certain style – a set of agreements. On the network it is a protocol. When working with E-mail, a number of protocols can be used. Among them:

• POP3;
• IMAP.

What is the difference, which protocol and in which case is it advisable to use it?

What is POP3

Wanting to send a letter or access a personal mailbox located on a remote server, the user can use the browser installed on the computer, which is not entirely convenient. More often used, which exchanges information with the server using a specific protocol. If it is Post Office Protocol, the process is as follows:

1. Compound;
2. The client receives information about the status of the mailbox, downloads letters;
3. Updating the server and deleting selected messages;
4. Closing the connection.

What is IMAP

The IMAP protocol provides the user with more options. After authorization on the mail resource, only the headers of the letters are downloaded to the computer. When you select the desired message, the client program downloads the entire letter. At the same time, you can work on-line and off-line. Read messages are not deleted; you can perform desired operations with them in the future.

Pros and cons of IMAP and POP3

Which protocol to choose? It all depends on the specifics of the job and needs.

In addition to the fact that messages are saved on the server without being deleted, the advantages of IMAP include:

• Possibility of access to the mailbox from several clients;
• Supports simultaneous access of multiple clients;
• Supports multiple boxes;
• Ability to create new folders that can be accessed by other users;
• Ability to mark emails as read, important, and others;
• Server search support;
• Possibility of working in on-line mode.

The only downside in this case is that the user spends more time downloading letters from the central computer.

Today we will tell you in detail about the most used Internet protocols - POP3, IMAP and SMTP. Each of these protocols has a specific purpose and functionality. Let's try to figure it out.

POP3 protocol and its ports

Post Office Protocol 3 (POP3) is a standard mail protocol designed for receiving emails from a remote server to an e-mail client.POP3 allows you to save an email message to your computer and even read it if you are offline. It is important to note that if you decide to use POP3 to connect to your mail account, emails that have already been downloaded to your computer will be deleted from the mail server. As an example, if you are using multiple computers to connect to one email account, then POP3 may not be the best choice in this situation. On the other hand, since mail is stored locally, on a specific user’s PC, this allows you to optimize disk space on the mail server side.

By default, the POP3 protocol uses the following ports:

• Port 110 is the default POP3 port. It is not safe.
• Port 995 – This port should be used if you want to establish a secure connection.

IMAP protocol and ports

Internet Message Access Protocol (IMAP) is an email protocol designed for accessing mail from a local email client. IMAP and POP3 are the most popular protocols on the Internet used for receiving e-mail. Both of these protocols are supported by all modern mail clients (MUA - Mail User Agent) and WEB servers.

While POP3 allows access to mail from only one application, IMAP allows access from multiple clients. For this reason, IMAP is most adaptable in cases where multiple users need access to the same email account.

By default, the IMAP protocol uses the following ports:

• Port 143– default port. Not safe.
• Port 993– port for secure connection.

SMTP protocol and its ports

Simple Mail Transfer Protocol (SMTP) is a standard protocol for sending mail messages via the Internet.

This protocol is described in RFC 821 and RFC 822, first published in August 1982. Within the scope of the RFC data, the address format must be in the format username@domainname. Mail delivery is similar to the work of a regular postal service: for example, a letter to the address [email protected], will be interpreted as follows: ivan_ivanov is the address, and merionet.ru is the postal code. If the recipient's domain name is different from the sender's domain name, then the MSA (Mail Submission Agent) will send the letter through the Mail Transfer Agent (MTA). The main idea of ​​MTA is to redirect letters to another domain zone, similar to how traditional mail sends letters to another city or region. An MTA also receives mail from other MTAs.

The SMTP protocol uses the following ports.

POP3 (Post Office Protocol) is an application layer standard protocol that is used by local email clients to receive data from a remote server over TCP/IP connections.

POP3 is used for remote interaction with an email server and downloading mail from a local email client. If you are accessing the same account from different devices, we recommend keeping the deleted copy items, as otherwise, the second device will download the email if the first one is already deleted. It should also be noted that POP3 is a one-way communication protocol, meaning that data is taken from the remote server and sent to the local client.

POP3 port: technology overview

The POP protocol supports download and delete requests for accessing mailboxes (called POP-RFC maildrop). The good thing is that most clients have the option of leaving mail on the server after downloading the email application using POP, connecting, generally receiving all the emails, saving them on the user's COMPUTER as new messages, deleting them from the server, and then disconnecting.

Other protocols such as IMAP (Internet Message Access Protocol) to provide more comprehensive and sophisticated remote access to types of mailbox operations. In the late 1990s and early 2000s, fewer than a number of Internet service providers supported IMAP due to the storage space required on the service provider's equipment.

Modern e-mail clients support POP. Over time, popular post office software has added IMAP support.Specifications

The server operates on the well-known port 110. POP3 SSL port is the latest standard in common use. Encrypted communication for the protocol is offered using the STLS or POP3S commands, which connects to the server using the transport layer security (TLS) layer or the secure sockets layer (SSL).

The client's available messages are recorded when the POP3 server port opens the mailbox and the effective message number, the location for that session, is a unique identifier assigned to the message. This parameter is persistent and unique to maildrop and allows the client to access the item in different sessions. Messages marked for deletion message number. When the client disconnects from the session, mail is then deleted by maildrop.

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 is updated by the RFC 2449 extension mechanism and the authentication mechanism in RFC-1734.

POP3 currently supports multiple authentication methods to provide varying levels of protection against unauthorized access to a user's e-mail address. Most of these are provided using POP3 extension mechanisms. Clients support SASL authentication methods with the AUTH extension. MIT's Athena project has also released a Kerberized version. RFC 1460 introduced APOP into the protocol. APOP is a challenge/response protocol that uses MD5 hash functions to avoid repeated privacy violation attempts.

POP4 exists only as an unofficial offering, adding workflow support, multi-message support, and message indicator control in competition with IMAP. 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 the extension and has confirmed that the role of POP3 is to provide simple support, primarily for loading 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 and Secure Sockets Layer protocol using the STLS command on a POP3 port rather than on another. Some clients and servers use the per-port method, which uses TCP port 995 (POP3S).

Demon on the Internet introduced an extension to POP3 that allowed multiple accounts to be combined on the same domain, and became known as Disabling POP3 Services (SDPS). To access each account includes the hostname, like john@hostname or john+hostname.

Kerberized Post Office Protocol

At checkout, email clients can use the Internet's Kerberized Post Office Protocol (KPOP) to receive email from a remote server over a TCP/IP connection. The KPOP protocol is based on the POP3 protocol with the difference being that it adds Kerberos security and runs on a default port number of TCP-1109 instead of 110. Version of the server software, on the Cyrus IMAP server. Comparison with IMAP

POP3 SSL port is a much simpler protocol which makes it easier to implement. Mail moves messages from the email server on your local computer, although you usually have the option to leave messages on the email server.

IMAP, by default, leaves a message on the mail server by simply downloading a local copy.

POP manages the mailbox as a single store and has no idea about the folders.

An IMAP client performs complex queries, queries the server for the headers or contents of certain messages, or searches for emails that meet certain criteria. Messages in the deposit dialog can be marked with various status flags (such as "deleted" or "replies"), 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 IMAP architecture implementation and system requirements, the manager, the user can record messages directly on the client machine, or store them on the server, or they can choose.

The POP protocol requires that the currently connected client only have one client connected to the mailbox. In contrast, IMAP allows simultaneous access by multiple clients and provides mechanisms for detecting mailbox changes to other concurrently connected clients.

When POP receives a message, it receives all of its parts, while IMAP4 allows clients to receive MIME parts separately - for example, to receive text without attachments.

IMAP supports flags on the server to track the status of a message: for example, if a message is read, if a reply is deleted, if a message is sent.

What are POP and IMAP, and which should you use for email?

If you already have an email client or application installed, you are faced with the terms POP3, SMTP and IMAP ports. 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 email account, the information below will shed some light on the matter. This article explains how POP and IMAP work and will help you decide which one best suits your needs.

Both messaging protocols allow you to read email messages locally using a third-party application. Examples of this are Outlook, Thunderbird, Eudora, libpng-dev or (Mac) Mail.

Source protocol POP. It was created in 1984 as a tool for downloading 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 simply caches (temporarily stored) emails in place. In other words, IMAP is a form of cloud storage.

What are the differences between POP and IMAP?

The two protocols are best compared based on their underlying operating processes.

POP operation process: connecting to the server; receiving email; local data storage; deleting correspondence from the server; disconnecting.

The default behavior of POP is to delete messages from the server. However, most clients also provide the option to leave a copy of downloaded mail on the server.

The default POP3 ports are: 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 summary and message content); processing user modifications, for example, marking read messages, deleting data; disconnections.

As you can see, the IMAP process is a little more complex than POP. Indeed, the folder structure and email messages are stored on the server, and a copy is stored locally. Typically, these local copies are stored temporarily. However, available for storage on a permanent basis.

Default IMAP ports:port 143 is port;port 993 is SSL/TLS port, also known as IMAPS.What are the benefits of POP?

Being POP in origin, the idea should be simplified that only the client requires access to email on the server, and that letters are better stored locally. This leads to the following advantages: email is stored locally, meaning it is always available, even without an Internet connection; an Internet connection is only needed to send and receive email; saves server space; the ability to leave copies of messages on the server; consolidation of multiple accounts email and mailbox servers.What are the advantages 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. This way, regardless of the device with which you log into your account, you will always be able to see the same structures, emails and folders, since 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 is stored on a remote server, accessible from multiple locations; to access your email, you must be connected to the Internet; faster browsing, because only the headers 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 the email protocol?

The protocol you choose depends on your specific needs and current work situation. The following points should help you make your final decision.

Choose POP if: You want to access your email using one device. You need constant access to your email, regardless of Internet availability. You have limited server storage.

Choose IMAP if: You want to access your email from various 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. You are worried about maintaining your emails .

If in doubt, consult IMAP. This is a newer protocol that allows you to be flexible and your email will be automatically reserved on the server. Plus, server space isn't usually an issue these days, and you'll always be able to store important emails locally. Mail client errors

If you notice the error, POP3, port: 995, security (SSL) number 0x800C0133 when trying to check your Gmail, then try compressing your mail folders. In the POP client, select File > File > Compress All Folders. This should resolve the issue.