On 8/2/23 05:08, Dr. Rolf Jansen wrote:

Am 07.02.2023 um 17:54 schrieb jeremy ardley <jeremy@ardley.org>:

On 7/2/23 22:01, Dr. Rolf Jansen wrote:

To begin with, usage of Amazons Simple Email Service (SES) is mandatory for outgoing mails from AWS-EC2 instances.

I run AWS-EC2 instances using postfix to send a receive mail. They can send direct assuming I set up suitable SPF, but they typically forward mail to another host under my  control that is not on AWS to use as the outgoing server.

OK, that’s another use case. Many do use a full fledged Postfix/Dovecot installation. However the outgoing port 25 into the internet is blocked by AWS, and therefore we may either use a third party relay for our outgoing emails or may use SES, which is not that bad - except some unusual peculiarities.

This is off topic, but to be precise:

- AWS throttles but does not block traffic to a *destination* port 25.

- The *origin* port on the EC2 instance is an unprivilged port, not port 25

- If you use a relayhost you typically send from an unprivilged EC2 port to port 587 on the relay host

Jeremy