What does “the following addresses had permanent fatal errors”, “550 Command RCPT User not OK” or “User unknown” mean?
This message is sent back to you, the sender, from the SMTP server. The server is telling you that the “user” you tried to send e-mail to does not exist. The user (user@domain.com) may have existed at some point in the past, but is no longer available. As people open and close e-mail addresses, this will happen. Once removed from the system on which they previously had an e-mail account, all e-mail sent to them will bounce back. A simple example would be sending e-mail to hih3720@Hostwire. Since we have no user setup under the login “hih3720”, the e-mail will bounce back immediately. In order to correct this problem, you will need to contact the recipient and obtain their new e-mail address.
