I am looking for some help - relative newbie!

What I see now is:

504 5.5.2 <diradmin@server1>: Sender address rejected:
need fully-qualified address

What I used to see was:

from diradmin by server1.mingmengtou.net with local (Exim 4.87)
(envelope-from <diradmin@server1.mingmengtou.net>)

So something has changed or I've inadvertently changed something.

I'm posting a thread because I after quite a bit of drifting around forum - I have not yet found a definitive answer.

I am now on Exim 4.92 and I've run the set_permissions script and both after a build update.

DNS is on my VPS providers servers - on looking at dns entries in the DA CP I note that local is no in red whereas every thing else is yes in green. Server IP changed recently - as far as I know all DNS entries updated but also I did a build update, etc after that and i can see a DA updated on July 13 which is when I think that the issue started. I believe this was an issue some years ago but I could not discern a clear answer for what to do.

I appreciate any help or pointers to the answer that I've yet to stumble across.

Thank you