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?
Post Office Protocol Version 3 (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 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 works ontwo 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 a 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 is best if you're going to be accessing your email from multiple locations, or if your messages are managed by multiple users.
IMAP protocol works on two ports:
- port 143 is the default unencrypted IMAP port;
- port 993 - must be used if you want to securely connect using IMAP.
What is SMTP?
The Simple Mail Transfer Protocol (SMTP) is the standard protocol for sending email over the Internet.
SMTP works on three ports:
- port 25 is the default unencrypted SMTP port;
- port 2525 - it opens on all SiteGround servers if port 25is filtered (for example, by your ISP) and you want to send unencrypted emails using SMTP;
- port 465 - this is used if you want to securely send messages 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. For example, Internet Explorer is 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 the correct settings in your email program. Most incoming mail servers use one of the following protocols: IMAP, POP3,
Outgoing mail server (SMTP)
This is a server used only for sending emails (to transfer them from yourmail client program to the receiver). Most outgoing mail servers use the Simple Mail Transfer Protocol (SMTP) 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 netgroup or not.
E-mail 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.
E-mail protocols: IMAP, POP3, SMTP and
Basically protocol refers to the standard method used at each endcommunication channel. 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 a particular email message, the 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. With anotherOn the other hand, you receive and download a lot of unsolicited messages (including spam or viruses) using this protocol.
SMTP protocol
SMTP (Simple Mail Transfer Protocol) is used by the Mail Transfer Agent (MTA) to deliver email 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 be able to use the SMTP protocol under certain conditions.
HTTP protocols
HTTP is not an email protocol, 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 is a good example of using HTTP as an email protocol.
Managed File Transfers and Network Solutions
Your ability to send and receive e-mail is mainly due to the 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 (such as Microsoft Outlook, Thunderbird, or Apple Mail) to an email server. It is also used to relay or forward mail messages fromone 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 a mail server to an email client. The 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 users' messages.
POP3 client receives email like this:
- connects to the mail server on port 110 (or 995 for SSL/TLS connections);
- retrieves email messages;
- 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 steps above are common practice.
IMAP
IMAP, especially the current version (IMAP4), is a more complex protocol. This allows users to group relatedmessages 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.
Working logic (imap4 settings):
- connects to mail server on port 143 (or 993 for SSL/TLS connections);
- retrieves email messages;
- is used to connect before closing the mail client application and download messages on demand.
Please note that messages are not deleted on the server. This can have serious consequences. IMAP specifications can be found in RFC 3501.
Choosing between IMAP and POP3
Because the basic function of SMTP is fundamentally different, the best protocol dilemma usually involves only IMAP and POP3.
If server storage space is important to you, 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, it's best 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, an Android tablet, a laptop and a desktop and want to read email from any or all of these devices, then IMAP is the best choice.
Synchronization is another benefit of IMAP. If you're accessing emails from multiple devices, you'll likely want them all to show whatever actions you've taken.
For example, if you read 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 put them in folders, it helps users better organize their correspondence.
Of course, all IMAP functionality comes 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. In fact, high CPU and memory usage can happen on both the client side and the 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 heavily depend on the end users. They would generally prefer to download all emails and not leavecopies of them 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 functions or features are more important.
Also, the way you want to access the e-mail client determines which protocol is preferred. 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 from different computers will prefer IMAP.
Spam firewalls with SMTP, IMAP and POP3
Most spam firewalls only deal with and protect the SMTP protocol. 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 foraccess to 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 allow email to be sent from the firewall.