EQ Forum Admin
Big Dan said:This message was created automatically by mail delivery software.
A message that you sent could not be delivered to one or more of its
recipients. This is a permanent error. The following address(es) failed:
SMTP error from remote mail server after RCPT TO:<email@example.com>:
host sbcmx1.prodigy.net [18.104.22.168]: 553 5.3.0 <firstname.lastname@example.org>... Addressee unknown, relay=[22.214.171.124]
This appears to be a standard user unknown error and not a blacklisting issue.
Are you sure the e-mail address was typed correctly?
If yes, and a second try fails..
I'd recommend calling the contact to get their current e-mail address, trying an alternate address, or if this is from a mailing list removing the invalid address from your list, whichever is most appropriate.