Description of problem:
/etc/dnf/automatic.conf has a command_email command_format example as follows:
# command_format = "mail -s {subject} -r {email_from} {email_to}"

This will not ever work with systemd. All you'll see is ". . . message not sent" in the dnf-automatic service status and no email will be delivered. The reason for this is that mailx will fork, dnf-automatic will exit, and systemd will kill the mail process. 

Version-Release number of selected component (if applicable):
dnf-automatic-4.2.23-1.fc32.noarch

How reproducible:
Always. I helped someone debug this and for both of us it failed to send an email every single time. I added -v to mailx and suddenly it worked. What I learned is that -v prevents mailx from forking. To do this without verbose output you can use the `-Ssendwait` option.

Steps to Reproduce:
1. Install dnf-automatic
2. Configure it to use the command_email emitter
3. Enable dnf-automatic-install.timer


Actual results:
Email never comes. If you look at the dnf-automatic-install.service logs you'll see '... message not sent'

Expected results:
Email is delivered as expected.

Additional info:
The default command and example in automatic.conf should be
command_format = "mail -Ssendwait -s {subject} -r {email_from} {email_to}"