We experienced an issue with automated email messages from a financial institution being rejected where the following was logged:
<snip> ruleset=CheckMessageId <snip> reject=553 5.0.0 Header Error
The associated Sendmail ruleset shows the following:
R< $+ @ $+ > $@ OK
I found that the institution's message-id did not contain the angle brackets. In order to permit messages from their domain, would I add the following rule?
R $+ @ example.com $@ OK