Port 25 reset

I already set port 587 as an alternate port but most smtp transactions come through port 25. I wonder if there is a way to configure the smtp stuff to arrive at my site on port 587.

port 25 is obsolete, try port 587 for smtp

Most ISPs block port 25, so I doubt it that will work very well, make port 587 the main one, everyone uses it now, what are you trying to setup?

So how do explain what I am observing in these tests that I ran?

I have both ports 25 and 587 forwarding to my mail server. Port 587 works fine if I try it manually from an external system, e.g. "telnet mydomain.com 587" but if I try the same thing on port 25, e.g. "telnet mydomain.com 25" it will timeout because port 25 is blocked. The latter was also tried from gmail and it doesn't get to my server.

Port 25 has not been used in probably better then 10 years, so you will not get it to work, there was so much spam going thru it everyone blocked it, it was all moved to port 587, I wouldn't put it anywhere in my config because its useless

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@danielsender wrote:

So how do explain what I am observing in these tests that I ran?

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As stated by others, Comcast deliberately blocks that port;

https://www.xfinity.com/support/articles/list-of-blocked-ports

I understand blocking port 25 for outgoing smtp transactions to avoid spamming, but I don't understand the purpose of blocking port 25 for incoming transactions.

Port 25 was never used for incoming mail, only outgoing along with port 587, incoming email uses port 110 for Pop3 and port 443 for imap, then if you want to use secure email, SSL, outgoing is port 465, incoming is pop3 is port 995 and imap is port 993,

FWIW, smtp only handles outgoing email, incoming is a another protocol, 

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@jlavaseur wrote: Port 25 was never used for incoming mail ...

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It was once used by customers of ISPs/mail service providers before spam abuse made it unusable for that purpose. It is still the port used by ISPs/mail service providers to exchange mail with each other. See https://www.grc.com/port_25.htm.