Undeliverable e-mail message from postmaster@he.local

I am responsible for IT for a small charity and we have a problem with a few individuals who e-mail us on our hosted e-mail addresses. The individual is on btconnect and our server is also on BT broadband and using MSExchange. I understand that the message from postmaster@he.local are generated by Exchange but can't tell whether this is a problem with our server (seems unlikely as most people send and receive e-mails perfectly well) or with the sender's server.

I have copied a sample test message below and would be very grateful if somebody can explain what is causing this problem.

I have * the personal details - hope that's acceptable but I don't want to compromise the individual's identity/security.

----- Original Message ----- From: "System Administrator" To: "****" <****.***@btconnect.com> Sent: Tuesday, April 06, 2010 3:26 PM Subject: Undeliverable: Test Message

Your message

To: ***** Subject: Test Message Sent: Tue, 6 Apr 2010 15:25:59 +0100

did not reach the following recipient(s):

***@quiltersguild.org.uk on Tue, 6 Apr 2010 15:26:07 +0100 The e-mail account does not exist at the organization this message was sent to. Check the e-mail address, or contact the recipient directly to find out the correct address.

From serverfault QGfisher

• If you have access to mail server log files, you can check if you find some lines regarding missing email. I think you don't find anything, because it seems a DNS mistake of sender server or an error in a mx server of your domain (there are two mx server for quiltersguild.org.uk domain).

  Regards Lorenzo

  From lg

• Are you sure that recipient's address is not misspelled? Double check it please.

  QGfisher : I have already done this. The address is fine.
  From Dmitry Trukhanov