postfix not listening on port 25, netstat shows nothing on port 25

Dovecot has no relevance to postfix not listening on port 25. They're two completely separate programs and one has no affect on the functionality of the other.

The simple way of explaining it is this:

Dovecot handles POP3 (110, 995) and IMAP (143, 993) ports for checking mail and postfix handles the SMTP ports (25, 465, 587) for sending mail. Note that port 465 is deprecated and you should use 587 (submission protocol) for secure SMTP.

Dovecot simply allows you to check the mail with a POP3 or IMAP mail client like Outlook or Thunderbird so it has nothing to do with postfix at all in your case. You likely don't have Dovecot 'enabled' unless you specifically downloaded and installed it yourself.

You might have to edit your master.cf file in postfix and uncomment the 'smtp' line at the top. This is usually the default setup in postfix so if you haven't changed anything in that file you may have to edit settings in your main.cf file. Check those settings to make sure everything matches up with your network/machine configuration.

Also, before you waste hours troubleshooting, changing settings and making things worse, make sure you check the most basic of things that you may have overlooked:

Is postfix even running?

systemctl status postfix

The result should be active (running) not inactive (dead), stopped or anything else with error messages.

To ensure postfix service starts every time you reboot the machine:

systemctl enable postfix

Unfortunately, without very specific information, it's difficult to help you since everyone's configuration is slightly different depending on OS, hardware, software settings, etc. Check the postfix logs for errors or any other messages that could give you some helpful insight into what's going on in your exact situation.

Other than that they claim postfix should work out of the box without having to change anything (but no worries it always takes me a bit of fiddling and finessing to get it working too.)

http://www.postfix.org/documentation.html

http://www.postfix.org/BASIC_CONFIGURATION_README.html