Suddenly getting Bad Helo - Host Impersonating Hostname error

I have been using POST Mail to send mail from my wordpress site. Suddenly yesterday I started getting a Bad Helo error 550. I’m being told that I need my “Outgoing Mail Server Hostname” domain to match what you are using to send the email. I am currently using my longhorn.mxrouting.net as the outgoing server. I’ve tried setting up my “mail.mydomain.com” as the outgoing SMTP server but then I get a “could not open socket” error. Any ideas on where to start.

Apologies for this, thanks for alerting me to it. This is a default exim ACL in DirectAdmin and is prone to re-introducing itself on updates. It should have been removed, and I’ve done so now.

Technically the ACL has a point, it’s just far too common that people use this particular configuration (not using a FQDN for HELO statement) for me to enforce it as a requirement.

Thank you for the quick response. I’ve checked and all is working as expected.

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