Sorry just a bit more info about the NDR, it comes back listing each recipient like so:
The following recipient(s) could not be reached: Bob Smith (E-mail) on 31/10/01 10:49 Unable to deliver the message due to a communications failure The MTS-ID of the original message is: c=GB;a= ;p=ORG;l=MAIL_SERVER-011031104908Z-8524 MSEXCH:IMS:ORG:SITE:MAIL_SERVER 3552 (000B099C) 552 Header line is ridiculously overlong Thanks, James. > Dear all, > > One of our users is receiving this NDR (as am I as the IMS Admin) when he > tries to send an e-mail to Mailshot distribution list he created. > > First he added each individual name in the 'To' field and it failed. Then > we created a distribution list (actually 2 of them to split them up) and > it failed again. There are around 160 e-mail addresses in total. > > Technet is no help, a search on google found a couple of articles but they > were a bit vague, due to one article we also tried putting the list into > the CC field but alas this was also in vain. There are no restrictions on > the users mailbox either. > > The server is 5.5 sp3 by the way. > > Any ideas my fellow Exchange administrators? Thanks. List Charter and FAQ at: http://www.sunbelt-software.com/exchange_list_charter.htm