What Port Does SMTP Use?
On the modern web, there’s not a single SMTP port. Instead, there are four common SMTP ports:
- 25
- 587
- 465
- 2525
Let’s go through them.
What is Port 25 Used For?
Port 25 was established all the way back in 1982, which makes it the oldest SMTP port.
Port 25 is still known as the standard SMTP port and it’s used mostly for SMTP relay.
What is Port 587 Used For?
Port 587 is the default port for SMTP submission on the modern web. While you can use other ports for submission (more on those next), you should always start with port 587 as the default and only use a different port if circumstances dictate (like your host blocking port 587 for some reason).
Port 587 also supports TLS, which means that you can securely submit mail.
What is Port 465 Used For?
Port 465 was originally registered for SMTPS (SMTP over SSL). After a brief stint in that function, port 465 was reassigned for a different use and deprecated.
Despite that fact, many ISPs and cloud hosting providers still support port 465 for SMTP submission.
What is Port 2525 Used For?
Port 2525 is not an official SMTP port (as recognized by the IETF or IANA). However, it’s still popularly used as an alternative to port 587 for SMTP submission and most ISPs and cloud hosting providers do support port 2525 for SMTP.
If port 587 is blocked, port 2525 makes a good alternative.