Happens sometimes... Some mail gets bounced and again from the same person it doesn't. Here is the last one sent to us from a whitelisted sender. He resent the message and it came through fine.
I'm sorry to have to inform you that your message could not be delivered to one or more recipients. It's attached below.
For further assistance, please send mail to postmaster.
If you do so, please include this problem report. You can delete your own text from the attached returned message.
The mail system
<firstname.lastname@example.org>: host mail.egearusa.com[188.8.131.52] said: 550 5.7.1
Unable to relay for email@example.com (in reply to RCPT TO command)
Final-Recipient: rfc822; firstname.lastname@example.org
Remote-MTA: dns; mail.egearusa.com
Diagnostic-Code: smtp; 550 5.7.1 Unable to relay for email@example.com