recently one senders from outside sent one email to one of my users in my server (our server is exchange 2007 and sourece server is exchange 2003 ) he receive following NDR :
do you know why he receive this NDR ?
Your message did not reach some or all of the intended recipients.
Sent: 1387/11/19 04:45 (.8
The following recipient(s) cannot be reached:
email@example.com on 1387/11/19 04:46 (.8
A critical function required for the transfer or delivery of the message was not supported by the originator of the report
<Mail.domain2.com #5.3.3 smtp;500 5.3.3 Unrecognized command>