This could be related to sendmail running instead of Exim. It looks like it's actually a *real* Sendmail that was running on your system before you replaced it with Exim package. Normally Exim handles Maildir creation automatically, and Ajenti V assigns mail:mail ownership to the mail directory.

You need to remove your old Sendmail instance and restart Exim4 SMTP server, which Ajenti V uses.

First, check that panel is listening: netstat -tlnp | grep 8000. If not, try running ajenti-panel -v.

Have you allowed CSF section access for your (non-root) user?

What?

This doesn't look right. Try fully restarting NGINX: service nginx restart.

Looks like you didn't stop Apache and it's still running. Check with netstat -tlnp | grep 80. Then kill the apache process by the found PID and restart websites from Ajenti.

Then your website path is probably set incorrectly. Check /var/log/nginx/<website>.error.log for details.