On 3/20/19 8:18 AM, Patrick Ben Koetter wrote:
* Yassine Chaouche <a.chaou...@algerian-radio.dz>:
Dear postfix,
I don't seem to get the idea of submission, I know I must be wrong, b/c so
many articles out there preach to use a different port for submission, but I
Use submission on TCP/587 for MUA to MTA traffic.
Use smtp on TCP/25 for MTA to MTA traffic.
Run authenticated MUA friendly policies on Submission. Run MTA policies on
smtp port.
Access providers may block outbound TCP/25 connections, because infected
enduser devices try to transport messages on that port to remote MTAs. They
won't block TCP/597 because submission requires SMTP AUTH, which requires the
sender to possess login/pass – something most spammers don't have.
p@rick
Note that submission on Port 587 is deprecated, it is now "official" to
use Port 465 with implicit TLS.
Using Port 587 isn't going to stop working, of course, but...
But anyway yes, port 25 is frequently blocked by consumer ISPs. It's
blocked by mine, for example.
