Hi,
you may want to check WHICH exim4 package is installed…
it has happened to me on a few machines that during upgrade exim4-daemon-heavy was purged and replaced with the light version - which then throws several errors…
Even tough in your case there seems to be nothing in your status, it may still be worth checking…
As Raphael said, your exim is NOT running (the indication in hestia is correct)…
PS: we do not need the “ls /var/log/exim4” - we need
cat /var/log/exim4/paniclog
cat /var/log/exim4/mainlog (which is ABSENT from your ls)
cat /var/log/exim4/rejectlog (which seems to have been archived without starting a new one?)
(cat could be replace with tail -200 or similar. or pipe through less)
IF paniclog is NON-zero in size it may show why exim is not willing to stay running…
HAPPY your problem was resolved. This seems to be a problem with the ubuntu upgrade - but it has also occurred when switching from MariaDB 10.5 directly to 11.x
IMHO your additional step is somewhat counterproductive…
When you install exim4 it does SYMLINK the sendmail to exim and ALL sendmail request are done through exim - I would prefer to keep it that way. I suspect that this desired behaviour is destroyed when you re-install sendmail… You can check by looking at /usr/sbin/sendmail (IF exim is installed this should be a symlink to exim4!)
ls /usr/sbin/sendmail
lrwxrwxrwx 1 root root 5 Nov 23 2022 /usr/sbin/sendmail -> exim4
Someone with more knowledge may chime in here, but that is the way I understand it.