What is Default SMTP Port Number? How to Choose right Port Number?

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Simple Mail Transfer Technology, or SMTP for short, is a widely used email transmission protocol. These protocols are used worldwide by internet mail servers to send and receive emails.

For instance, your email client is required to upload an email to an outgoing mail server. Your email will then be forwarded to the recipient's incoming mail server via the outgoing mail server.

SMTP ports are crucial in the Simple Mail Transfer Protocol (SMTP) submission process. Because of this, it's crucial to select the proper port when establishing an email server. Errors in email sending and receiving may be caused by incorrect settings.

The Internet Engineering Task Force (IETF) received a proposal from the University of Southern California in 1982.

The publication of Request for Comments (RFC) 821 designated port 25 as the standard transmission route for internet email.

Even now, 40 years later, we still primarily transfer email between two mail servers using port 25.

A few others have superseded the first SMTP RFC. However, the foundation for SMTP connections stays the same or is somewhat comparable.

What purpose do SMTP ports serve?

SMTP ports are communication endpoints that manage data transfers from one server to another. In contrast, SMTP is a mail submission protocol that enables users to send emails over the internet.

It's necessary to configure an email account before you can begin using an SMTP server.

To correctly route your emails, specify an IP address and a port number. Emails must go through three stages before they are sent to their intended recipient:

Sending emails to an outgoing mail server is known as email submission.
Then, choosing which port to use would be best because this occurs over SMTP.
They are finally relaying communication between two mail servers through SMTP. Users typically don't need to set a port for it because it utilizes a default one.

Receiving emails means that the messages reach the recipient server.

The Internet Message Access Protocol (IMAP)/Post Office Protocol 3 is in charge of this procedure (POP3)

Why is there more than one port for SMTP?

Several processes are involved in sending emails from one client to another. First, you must submit the email from your client to the mail server. After that, it must be relayed from one server to the next before being received by the recipient's email client.

Various ports are involved in each step of this process. You must enable mail delivery on the common port 25 if setting up your mail servers to accept mail from outside systems (such as Gmail, Yahoo, etc.).

Mail servers only know how to transfer or relay mail on this port.

The narrative is slightly different for mail submission, though. A mail client will often connect on a different port when it wants to submit a message for the relay.

Typically, port 587 will be used for this. A separate port is employed even though the email client and server utilize the same protocol (SMTP).

The process of receiving the email does not use SMTP. The protocols utilized to receive an email, IMAP or POP, also rely on certain ports.

But why are there multiple ports if email submission and transmission both occur through SMTP? This is due to a few historical factors:

Numerous internet service providers started limiting port 25 for sending mail to other systems to stop users from creating spam and delivering it through their networks.

This prevents a great deal of malicious mail from being transmitted via consumer-level/residential connections since receiving servers typically only allow mail on port 25.

A mail server must ascertain when a connection is created whether the client wants to send a message to be transmitted to the server or wants the server to relay the message to another SMTP server.

Administrators of mail servers can implement various limitations and authentication requirements for each type of interaction by using a distinct port.

Different types of SMTP ports

To assist you in selecting the ideal port for your SMTP server, we will discuss the functions of SMTP ports and go over four of them.

Port 25

SMTP port 25 was initially designated as the default transmission channel for emails by the Internet Engineering Task Force (IETF). The main application of SMTP port 25 is still SMTP relaying.

We don't advise utilizing it as a mail submission channel, even though the Internet Assigned Numbers Authority (IANA) still identifies it as the default SMTP port.

Viruses and spam have been spread through port 25. Additionally, messages sent through port 25 are not encrypted; they are transmitted in plain text.

This raises many security risks because threat actors could intercept unencrypted data.

Many web hosts and ISPs (internet service providers) have consequently decided to ban all port 25 traffic. This is done to lessen the number of spam emails sent through it.

Despite this, port 25 is a useful channel for troubleshooting connection testing and email settings.

When setting up the contact form for your website, for instance, if the server won't answer via port 25, it means the problem isn't with the SMTP server.

Modern SMTP email applications (such as Thunderbird, Mail, Microsoft Outlook, and others) shouldn't often use this port.

Residential ISPs and cloud hosting companies typically block it to reduce the spam sent from infected machines or servers.

It would help if you didn't have any traffic passing via this port on your PC or server unless you're specifically running a mail server.

Avoid utilizing port 25 when using SMTP for a WordPress website or email client setup because most home ISPs and cloud hosting companies restrict it.

Unless you're running a mail server, there shouldn't be any traffic going over this port on your server.

Port 465

As a replacement for port 25, IANA developed SMTP port 465. Utilizing a Simple Mail Transfer Protocol over SSL enables secure email transmission (SMTPS).

It was never acknowledged as an official SMTP port by the IETF.

Mail transmission on port 465 is protected by implicit TLS, which encrypts the initial connection using a TLS or SSL certificate.

SMTP port 465 is no longer recommended and is not acknowledged as a standard for mail submission. Only when your hosting provider demands the protocol do we advise utilizing it.

Port 587

As a replacement for channel 465, SMTP port 587 was introduced. It is acknowledged as the current primary port for email submission by both IANA and IETF.

Since STARTTLS is supported on SMTP port 587, SSL and TLS encryption are also supported. It enables safe message submission and adds extra security against viruses and spam.

A protocol command called STARTTLS is sent between an email client and a server. It encrypts data transferred through TLS connections.

Additionally, SMTP authentication provided by STARTTLS necessitates SMTP client login with the mail server to access the system.

Port 2525

Modern protocols are used to connect to SMTP servers on port 2525. Since it offers TLS encryption for email transmission, it is regarded as a secure solution.

It is now a widely used port that is supported by a large number of ESPs, ISPs, as well as cloud hosting services.

Port 2525 is occasionally used to set up virtual private servers (VPS). If you experience connectivity problems while submitting an SMTP message, port 2525 primarily acts as a backup.

Try using port 2525 instead of port 587 if your connection is being rejected or blocked when you use port 587.

Port 2525 is not a standard channel. Hence the IANA and the IETF do not actively monitor it because they do not recognize it as an acceptable SMTP mechanism.

However, some hosting companies don't support it as, well.

Which port should you use for SMTP?

As we've already discussed, picking the right SMTP port is crucial.

Port 587 is nearly always the ideal option for configuring your WordPress website or email client to send emails over SMTP (submission). It is the standard SMTP port for submission and enables a secure TLS connection.

Port 2525 is a typical substitute if port 587 is banned. Although this SMTP port number is not formally recognized, most web hosts support it and extensively use it.

Although SMTP port 465 is still supported by many providers, it is no longer regarded as a standard. Use ports 587 and 2525 instead.

Last but not least, even though port 25 is frequently used for SMTP relay, you must avoid using it when installing an email client or a WordPress website since most ISPs and cloud hosting providers block it.

Conclusion

Simple Mail Transfer Protocol, or SMTP for short, is the method used to send emails over the Internet.

Computer ports are the means through which separate computers join a network and carry out electronic operations. A port created to send an email over a network and to its receiver is an SMTP port.

Of course, numerous SMTP ports might be utilized, just as there are numerous computer ports.

Start with port 587, the default port for SMTP submission, whether you wish to utilize SMTP on your WordPress website or in your email client.

If port 587 isn't functioning, you might try port 2525. It is often used and supports TLS for secure communication even though it is not an authorized SMTP port.

We hope that this guide has assisted you in selecting the proper SMTP port.