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What is Port 2525?
Written by
Dibya Sahoo

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What is Port 2525?

Port 2525 is used for secure submission of emails for delivery by modern ESPs. Unlike other SMTP ports, you will not find the port block issue with port 2525. As this is a non-standard port for SMTP, so it is not getting monitored extensively and are allowed on consumer IPs and Cloud hosting providers like Google Compute Engine. It is not an official SMTP port and it is not sanctioned by the IETF nor IANA. It is an alternate port which has the same functions as port 587.

Pepipost supports TLS on port 2525, this you can verify by connecting to and issuing an “ehlo” command. 250 STARTTLS in output confirms that the endpoint accepts TLS connection requests.


How to check if Port 2525 is blocked on your network?

There are some common error messages which you might encounter;

  • 2014-08-31 17:13:00 SMTP ERROR: Failed to connect to server: Permission denied (13)
  • Connection unexpectedly closed: timed out
  • Timeout::Error (execution expired)
  • S: SMTP ERROR: QUIT command failed: Connection: closed
  • SMTP connect() failed.
  • Mailer Error: SMTP connect() failed.
  • SMTP -> ERROR: Failed to connect to server: Connection timed out (110)
  • SMTP Error: Could not connect to SMTP host.

There can be more… this is just a sample list. All these are errors from different programming environment, but all lead to a common problem that your outgoing port 465 might be blocked.

There are multiple ways to check if a particular port is blocked on your network, the simpliest one to check this is using the telnet command on your terminal as shown in the above screenshot. If Port 2525 is blocked, you will get a connection error or no response at all.

telnet: connect to address Connection refused
telnet: Unable to connect to remote host

There is one more tool outPorts on Github, which is very user-friendly when it comes to checking the outbound ports. But, yes it has multiple dependencies that need to be installed to start using.

Once, installed just run the below command to check if the port is opened or closed:

outPorts 25

When to use it?

Most ESPs support the use of Port 2525 as an alternative to port 587 for SMTP. Port 2525 also support TLS encryption.

Difference between port 2525 and 25/467/587

Port 2525 is it as an alternate port, which mirrors port 587, in the case the other mentioned ports are blocked.Port 25 is the default port used for replaying.Port 467 is the port chosen for encrypted connections.Port 587 is used for the secure submission of email for delivery by modern email servers.
This port also supports TLS encryption.Port 25 is blocked due to the risk of spam and malwarePort 465 should no longer be used at all.Port 587 coupled with TLS encryption is the best way to ensure that any email is submitted securely and reliably.
This port is not endorsed by the IETF nor IANAIANA still recognizes Port 25 as the standard, default SMTP port.The port is no longer recognized by IANA.This port has secure according to  the guidelines set out by the IETF.

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