Sendmail requires hostname when sending/receiving emails
I was running fine on Redhat 8.0, I had some other problems, so I just decided to re-install the OS to 9.0. I backed up all my configuration files, etc and copied them back into place. Everything seems to be up and running fine again, except for one thing.
The problem is with sending/receiving mail. For example, I have a user named "alex" If I try to email email@example.com, it bounces.
If I use firstname.lastname@example.org, it works.