Det viser sig faktisk at Meebox servere er blevet blacklistet:
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:
xxx@yyy.zzz SMTP error from remote mail server after RCPT TO:<xxx@yyy.zzz>: host mail.yyy.zzz [69.195.124.137]: 550-Message rejected because (web8.meebox.net) [77.66.30.208]:45057 is 550 blacklisted.