I have a few users trying to send email to a client and his secretary. They've been sending to them fine and just a couple of days ago they started getting NDRs when they send to them. I spoke with a tech from that company and he assured me that nothing changed for them and that they receive emails from others just fine. I looked on MS KB and while I did find some articles, none of them were helpful. Below is the message received when we try to send to this company: Your message did not reach some or all of the intended recipients. Subject: Test Sent: 10/16/2002 12:09 PM The following recipient(s) could not be reached: '______________' on 10/16/2002 12:09 PM The recipient name is not recognized The MTS-ID of the original message is: c=US;a= ;p="organization";l="server"-021016160847Z-910 ****************** I can't figure out what happened. I double-checked their email addresses - they were correct. We can receive mail from them without a problem, but if we try to reply we get an NDR. Any help would be appreciated. Thanks Delores **************************************** The information supplied in this message may be legally privileged. If you are not the intended recipient of this message, the sender does not intend delivery to you to waive any privilege or right pertaining to this message. If you have received this message in error, please immediately notify the sender by return e-mail, and delete the errant message. Thank you.