Problem with sending mail

[malamba]

I Have microsoft exchange server 5.5 which has been working fine. Of late all outgoing mail is being returned. We are only able to send and receive within our domain and are able to receive from other domains e.g. yahoo but we cant send outside our domain. The message i am getting on my outlook express client is as follows:
====================================================
Your message

To: Dickson Malamba
Subject: Re:
Sent: Tue, 23 Nov 2004 10:52:23 +0200

did not reach the following recipient(s):

Dickson Malamba on Tue, 23 Nov 2004 11:18:04 +0200
The recipient was unavailable to take delivery of the message
The MTS-ID of the original message is: c=us;a=
;p=co;l=MTLNETWORK0411230902X3NFQ23T

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I dont know why microsoft is un able to send mail outside the domain? Please help.

 

[Airborn112]

Try checking to see if your dns went down or expired.

 

[Zelandakh]

Outlook Express?

 

[dennisbbb]

The recipient's mailbox has exceeded both Warning Limits and Prohibit Send Limits. There is nothing you can do until they clean out their box.