I have some error messages when sending mails to some addresses: 550-Callout verification failed: 550 550 5.1.1 User unknown (in reply to RCPT TO command) Can anybody tell me what to do?
To which addresses are you trying to send - as in provider ? Microsoft is known to be problematic. What is the full output of the log entry in /var/log/mail log when you're sending these emails ? Looks like your destination address does not exist or its conflicting somehow with the spam filters on the receiving end. That, or something wrong with your headers ?
