I have an email address which forward incoming emails to a ticketing system, suddenly the forwarding rule stopped working. I have tried several email relays but they all failed.
Apparently, EXIM changes the from address to the sender’s email address that’s why the SMTP provider reject it as it’s not verified.
That sounds like the from address is not changing, which is good, if you hope to open tickets for the senders. You need to configure your ticketing system to accept all email from your HestiaCP mailserver. You should not be testing messages from what is effectively a trusted internal relay.
See if my old post can help you.