Email problems since last update

Hi, is anyone else having trouble with mail since the last update?
At first my mail was not working at all but I tracked that down to the postfix service not being installed for some reason. So I manually installed that again and can now receive email but when any of my domains try to send email it immediately gives an undeliverable mail message with the following details attached

Reporting-MTA: dns; localdomain.com
X-Postfix-Queue-ID: C7BD7BA152
X-Postfix-Sender: rfc822; aaron@localdomain.com
Arrival-Date: Fri, 23 Apr 2021 15:29:02 +0700 (+07)

Final-Recipient: rfc822; aarontharker1972@externaldomain.com
Original-Recipient: rfc822;aarontharker1972@externaldomain.com
Action: failed
Status: 5.1.1
Diagnostic-Code: x-unix; user unknown
I’ve tested the server can resolve the MX records using nslookup and even manually sent a test message to the same external domain via telnet without any issues

It almost seems like the MTA thinks all domains are local and is not looking for DNS addresses at all. I have checked the server can resolve DNS through nslookup and SSH. I have even manually sent email to a few of the domains it was rejecting from via telnet. I can’t see anything wrong in the logs except for a message about Razor2 checks failing but that is incoming email scanning so can’t see it having anything to do with it.

no one has any ideas?