I switched to mails under domain I own (and powered by FastMail) some time ago; I now use alias@username.mydomain form. Try to filter for that without breaking non-aliased e-mails!
By that point you might as well set a fixed-width length and treat everything after that as an alias, like me@domain.tld would be the base and mespammers@domain.tld would be your alias for spammers.com, etc. Even better, put the alias before the username and keep the + as a separator.