Ytdyklly

I need to understand..
I am trying to put on mail service on my Postfix/Ubuntu station using .
Provided that my ISP has blocked port 25, I targeted to use port 587 instead.
So, I made changes in main.cf as recommended:

relayhost = [smtp.gmail.com]:587

smtp_sasl_auth_enable = yes

smtp_sasl_password_maps = hash:/etc/postfix/sasl_passwd

smtp_sasl_security_options = noanonymous

smtp_tls_CAfile = /etc/ssl/certs/ca-certificates.crt

smtp_use_tls = yes

So far, I was able to send Emails through my Google account. But I could not receive any!
To investigate about this issue, I monitored the listening activity on different ports, and I noticed that Postfix has initiated its listening process “master” on port 25 only!

I am a bit confused, since nothing stayed in the configuration files referring to port 25.
To be sure about the usability of the port 587 by Postfix, I issued the command to Firewall:

ufw allow any to any port 587 app Postfix

fw answered me that it would not repeat adding an already existing rule.
But when I list active rules, the rule I emphasized does not appear in the list!

I realy confused : Postfix only listens on 25, fw does not figure out a rule I issued, mails does not reach my station!
Help, clarifications !

First, the shown configuration has absolutely nothing to do with what ports Postfix listens on. All settings that you show – relayhost and all smtp_* parameters – apply to Postfix acting as client, i.e. when it sends outgoing mail to external domains. (As you've said, this part works fine.)

For incoming mail, the ports to listen on are configured in master.cf – 587 is titled "submission" there, as in, it's the port which clients use to submit new messages. (Note that it requires authentication by default, so it'll take some more configuration to make it suitable for accepting inbound mail from servers. In fact, it might be better to add a new port entry, e.g. port 26, for inbound mail.)

However, in the end that won't do anything useful, because other mail servers do not magically know what ports your system is listening on for SMTP. There is no way to tell Gmail or other domains to deliver you mail on a nonstandard port – they will always attempt to connect to TCP port 25. (The only exception is systems which you administer.)