Why is my email sending using my hostname not my mail mx?

[alanms]

Following advice here, my server's hostname is something like server.domain.tld - in my case it's vps.domain.tld

I recently had a problem where most of my email worked, but some emails to certain domains got lost in the void - they sent (confirmed in exim logs) but were never received, not even as spam, with no delivery reciept. The first clue I had that anything was wrong was when clients started chasing me to send them things I'd already sent them days ago.

I used an online email testing service and it seems the problem was this:



I'm confused. vps.domain.tld is only used as my server hostname. None of my email settings mention it.

Why is my mail server using the server hostname as the sender instead of the mail server domain in the mx record? And what do I need to change to make these match?

I have multiple domains on this server, and each will have their own email accounts. I want each to use its own domain as the sender, and none to use the server hostname.

[tjebbeke]

The hostname is always used, you also need to create an reverse DNS record from your IP to your hostname.