I have been managing my websites and having seperate emails for each different domain. The bad thing about emails is that you are faced with the possibilities of getting spam emails from spammers. And let’s be honest, those spammers are not stupid people, and they know how to use whatever proxy or blackbox they have back in their underground secret tunnel to send us their useless piece of garbage in their best possible ways
If you happen to have cpanel with your hosting company, you’re in good luck. Cpanel comes with a spam filter manager (or whatever the right term is) called SpamAssassin that helps you to filter out potential spam. Just remember to enable it in cpanel-> Email -> SpamAssassin and it will protect all your email accounts (main account as well as those for the addon domains).
However there were still several occassions where some were able to get through. And to get get rid of those as well, you can set filters in cpanel-> Email -> Email Filtering to filter out potential spams based on either the subject, body or sender.
Doing this has been able to keep my emails clean from spam most of the time.