You generally avoid sending to known bad addresses or your reputation will be destroyed very quickly. The 550 response is (read: was) a clear "you fucked up, th

You generally avoid sending to known bad addresses or your reputation will be destroyed very quickly. The 550 response is (read: was) a clear "you fucked up, this user doesn't exist" prior to this. I saw someone on Reddit say his SES was suspended for sending tons of bounced emails in a short period of time - it's taken very seriously by ESPs. E: also user rtx a few comments below