How to find the port number of a mail server

There are a few ways to find the port number of a mail server:

  1. Check the mail server's documentation: If you have access to the mail server's documentation or configuration files, you can look for the port number specified for the mail server.

  2. Use the telnet command: You can use the telnet command to connect to the mail server and see which port it is listening on. For example:

    telnet mailserver.example.com 25

    This will attempt to connect to the mail server on port 25 (the default port for SMTP). If the connection is successful, you'll see a response from the mail server. If not, you can try other common ports like 587 or 2525.

  3. Use the nmap command: nmap is a network scanning tool that can be used to scan a mail server and identify the ports it is listening on. For example:

    nmap -p 1-65535 mailserver.example.com

    This will scan the mail server for open ports from 1 to 65535. Look for the port number that corresponds to the mail server's protocol (e.g. 25 for SMTP, 143 for IMAP, etc.).

  4. Check the mail server's configuration files: If you have access to the mail server's configuration files, you can look for the port number specified in the configuration files. For example, in Postfix, you can check the master.cf file for the port number.

  5. Use a mail client: You can also use a mail client like Microsoft Outlook or Mozilla Thunderbird to connect to the mail server and see which port it is using. For example, in Outlook, go to File > Account Settings > Server Settings and look for the port number specified for the mail server.

Common port numbers for mail servers:

Note that some mail servers may use non-standard port numbers, so it's always a good idea to check the documentation or configuration files to confirm the port number.