"Message delayed" messages TO only one sender in the domain
I am the administrator of a small company running a SBS2011 server with 30 user connected to LAN with Win7+Off2010.
EVERY TIME one specific user is sending a mail to foreign mail addresses, she gets a message return saying that the message she tries to send is delayed.
If her colleague sends the same email to the same recipient it goes through without any problems.
This is the entire error message:
"Reporting-MTA: dns; SERV-SBS.INTERNALDOMAIN.local
Final-recipient: RFC822; NAME@DOMAIN.de
X-Supplementary-Info: < #4.4.7 smtp;400 4.4.7 Message delayed>"
Normally I would say, that this was an indication of a problem in the receiving end, but then WHY is it only one of my user who is getting these messages?