I have several VPSes to a provider which recently started throttling outgoing SMTP connections to prevent spam.
While this is not such a big issue, sometimes mails gets delayed for obvious reasons. Mainly mailing list delivery and multi recipient mails. For example if I send a mail to 8 recipients (the outgoing connection limit is 5/s) I get throttled with connection refused errors:
-Queue ID- --Size-- ----Arrival Time---- -Sender/Recipient------- CC7E3E2000C 50569 Fri Aug 3 10:37:10 firstname.lastname@example.org (connect to YYY-com.mail.protection.outlook.com[22.214.171.124]:25: Connection refused) daniele@YYY.com elisa@YYY.com evely@YYY.com chlara@YYY.com nite@YYY.com redine@YYY.com tori@YYY.com rachele@YYY.com vatecka@YYY.com
First, I thought Postfix would reuse the same MX connection for a domain... But if the connection is blocked it means it's trying to make more than 5 different connections.
I tried delivering also a mailing list and it's not that bad (given the limited number of recipients that I have).
Is it possible to adjust the configuration so the 5 connections/s limit is not reached?