Best practice for SMTP relay with user authentication

[Erik Norgaard]

Hi:

I have my postfix authenticate users before accepting mail for non-local 
delivery. Till now, users can connect to port 25 and 465 (smtps) use 
STARTTLS and authenticate.

But, I stumbled upon submission port 587 which is not reserved - it 
appeas - for a protocol but for a use?

I'd like to align my configuration with best practice. Should I just 
move postfix to bind to port 587 or did I misunderstand that submission 
is indeed a different protocol? Is there any best practice for which 
protocol should be used for submission?

Thanks, Erik

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