That’s unusual! It sounds like it may have gotten deleted somehow… in any case, you can see what the contents of the procmailrc should be in the “procmail” section of the manual install guide:
On Virtualmin systems, emails should be delivered to $HOME/Maildir.
If that’s not what you’re seeing, you may want to look at the email logs to see what’s going on with email delivery.
Your email logs are located in either /var/log/maillog, or /var/log/mail.log, depending on your distro. Also, your procmail log may help too, that’s in /var/log/procmailrc.
As far as outgoing email goes – do you receive any bounce messages? But, same thing there, you’d likely want to review your mail logs to see what that’s not working.