While its a pretty brute force approach, one method Iâm trying is to curtail the source of email. In otherwords, if smtp traffic comes from an unknown source it gets directed to a sendmail server that intentionally rejects the email message (550 with a informational message/url).
1) You send bounces from spammers to innocent people, whose addresses have been forged.
This is an SMTP reject, not a bounce. It's a lethal variety of greylisting. This technique works great to keep spam out of your mailbox.
3) You are dropping valid emails.
Right. It also quite an effective way to be sure you never hear from non-technical users who don't understand your bounce message, and from people like me who don't feel like jumping through your hoops, particularly in a case like this where we're responding to a question you asked. R's, John