I use Rustdesk to access PCs and embedded devices from other PCs and embedded devices. Mostly doing remote support to avoid driving.
It’s easy to set up with a container-based server.
I don’t have to care about licenses and crap like that. It just works.



First layer is done by Postscreen (by Postfix). It watches bots misbehaving, check blackhole DNS and disconnects them. Fail2ban takes care of bots who cause errors and warnings in logs and bans them. Third layer is SPF and DKIM. If it does not match, it’s getting flagged.
If someone conforms to protocols and passes the tests, there is still rspamd on the fourth layer. It does zillions of checks on the metadata and additionally learns via bayes. Dovecot moves all the crap to Junk and inserts the valid mails into their proper folders.
The fifth layer is me. If some junk mail arrives in the inbox, I move it to Junk manually and Dovecot tells rspamd to learn it as spam.