Set the port in an smtpd entry in the master.cf file. You can change the existing smtpd entry or add an additional one depending on what you need.
An entry like the following causes Postfix to listen on port 10025:
10025 inet n - n - - smtpd
Article ID: 123, Created: 4/23/2025 at 4:05 PM, Modified: 4/23/2025 at 4:05 PM