We have mixed domain, Exchange 2003 SP2 Build 7638.2 and also Exchange 2007 Rollup 11 SP3.
On Exchange 2003 Server :- On 2nd Feb 2014 only one security update was installed for Windows Server 2003 (KB2914368)
Some Users on randomly basis are unable to send e-mails from 2003 exchange to 2007 Exchange users Internally.
They are sending mails from outlook and users from 2007 to 2003 dont have any issues.
But sometime mails from 2003 to 2007 goes without any issue.
The NDR reported is as below.
From: System Administrator
Sent: 22 February 2014 15:59
Subject: Undeliverable: Regarding Test Message
Your message did not reach some or all of the intended recipients.
Subject: Regarding Test Message
Sent: 22/02/2014 15:59
The following recipient(s) could not be reached:
XXX,XYZ on 22/02/2014 15:59
The message contains a content type that is not supported
<HubServer.Domain.UK #5.6.0 smtp;554 5.6.0 STOREDRV.Deliver.Exception:PropertyValidationException; Failed to process message due to a permanent exception>