Re: Postfix and local mail redirection

[Sad Clouds <cryintothebluesky%gmail.com@localhost>]

On Mon, 25 Nov 2024 12:21:26 -0800
"Greg A. Woods" <woods%planix.ca@localhost> wrote:

> Note here the receiving system answers on the "submission" port, not
> SMTP, but I don't have any authentication set up for mail submission.
> 

Thanks for info. As far as I understand services on ports 25 and 587
use the same SMTP protocol. Port 25 is recommended for mail relaying
and port 587 is recommended for mail submission. What is the difference
between the two? You can probably think of mail submission as relaying
that mail through a particular SMTP server to its final destination.

I'm thinking SMTP clients connecting to port 587 are forced to always
use TLS and authentication. These would be normal users sending email
to the Internet. On the other hand, SMTP servers delivering mail to
port 25 may not be configured for TLS and authentication, hence
enforcing those policies could result in undeliverable mail. Are these
the main reasons for two separate ports?

In other words, SMTP protocol does not support different types
of "streams" e.g. relay or submission, hence as an afterthought, port
587 was designated for submission only. Is this correct?