I have been asked to investigate a problem with undeliverable emails. The problem is that email to a particular domain is not being sent but all other emails from the same server are apparently working correctly. The administrator of the receiving domain insists that our server is not handing the mail off correctly to the internet. Our set-up consists of a windows network using a windows 2003 server domain with a gateway server running Fedora 9 and using Sendmail 8.14.12. Both servers are due for replacement in the near future. Mail transport from Outlook on the windows network appears to have no problem using the mail server, only in the case of this one particular domain does delivery fail. I have tried sending an email to the "undeliverable" domain and cc'ing it to another external address. The message failed on one address but succeeded immediately on the other. The entry in the sendmail log is as follows:

Apr 19 11:51:03 gw sendmail[467]: q3J1p3w2000467: from=<Administrator@yyyyy.com.au>, size=1510, class=0, nrcpts=2, msgid=<64001D94702C3545B284436BFA4D2932457EAB@xxx.yyy.local>, proto=ESMTP, daemon=MTA, relay=[192.168.xx.xx] Apr 19 11:51:04 gw sendmail[470]: q3J1p3w2000467: to=<xxx@zzzz.com>, delay=00:00:01, xdelay=00:00:01, mailer=esmtp, pri=151510, relay=extmail.zzzz.com. [xx.x.xxx.xxx], dsn=2.0.0, stat=Sent (Message received: 20120419015104.WMYJ5617.nskntingx06p.mx.zzzz.com@gw.yyyy.com.au) Apr 19 11:51:07 gw sendmail[470]: q3J1p3w2000467: to=<AAA@BBBB.com>, delay=00:00:04, xdelay=00:00:03, mailer=esmtp, pri=151510, relay=BBBB.com.inbound15.CCCCC.net. [xxx.xx.xxx.xx], dsn=4.0.0, stat=Deferred: Connection refused by BBBB.com.inbound15.CCCCC.net

dig finds the correct MX entries for the outside domain and traceroute has no problems locating the foreign server. Any suggestions would be gladly received. Thanks Michael