Ubuntu: How to change Dovecot / Postfix POP3 default port to 110?

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http://serverfault.com – I was trying to log in to my email from Gmail POP3 feature and I had to try every single port to connect to my mail server. What's the command on terminal or what file I have to change the Dovecot/Postfix default port to 110 instead of 995? Can I change the port to be some other number? (HowTos)