On Mon, 25 Nov 2024 12:21:26 -0800 "Greg A. Woods" <wo...@planix.ca> 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?
