Aws workmail, if I recall it’s 5$ per user + storage. Will be cheaper then any ec2 instance and you get some spam protection also. Users can also have multiple emails.

I think this is the wrong approach (self-hosting a mail server). Just use a dedicated service like MxRoute, Migadu, FastMail, StartMail, or similar. Heck, even Google Workspaces and Microsoft 365 are a better option. That's my $0.02, anyway ;-)

Fuck these bot posts.

If you only need a receiving and catch-all address. You could use Cloudflare’s relay service. It’s totally free with the exception that you can’t send email but only have them forwarded to another email address, such as your personal email address.

It’s super easy and quick to setup, and if your domains aren’t already behind Cloudflare you should do it, it really is great.