Recieving System Undeliverable from Internal User

I have a user who cannot recieve emails from certain internal users inclusing me.  Everytime I send an email to him I get a message saying:

Your message did not reach some or all of the intended recipients.

      Subject:      test
      Sent:      01/11/2006 10:05

The following recipient(s) could not be reached:

      xxxy.xxx@xxx-x.com on 01/11/2006 10:05
            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.
            <dxx.xxxx.xxx #5.1.1>

I have also sent an email from my hotmail account and  recieve an undeliverable message from postmaster.  I'm not sure why he's not recieving emails.  I've resetted his account and mailbox.  

I don't know where else to look.

I've done a message tracking from me to the affected user and it is as follows:

- <TrackHistory xmlns="http://www.microsoft.com/schemas/MessageTracking">
- <Exchange_MessageTrackingEntry>
  <TimeLogged>2006-11-1 10:05:22</TimeLogged>
  <OriginationTime>2006-11-1 10:05:22</OriginationTime>
  <KeyID>\\delta.Exponential-e.it\DELTA.log\20061101.log,5557461</KeyID>
  <LinkedMessageID>c=GB;a= ;p=Exponential-e;l=DELTA-061101100522Z-1505</LinkedMessageID>
  <MessageID>DD28797B4AA4C34BAFF5CBF96740815C0EEA78@delta.Exponential-e.it</MessageID>
  <SenderAddress>EX:/O=EXPONENTIAL-E/OU=FIRST ADMINISTRATIVE GROUP/CN=RECIPIENTS/CN=ADEEL.AHMAD</SenderAddress>
  <ServerName>delta.Exponential-e.it</ServerName>
  <Subject>test</Subject>
  <EntryType>1027</EntryType>
  <RecipientCount>1</RecipientCount>
  <Priority>0</Priority>
  <Size>11337</Size>
- <Recipients>
- <Recipient>
  <RecipientAddress>carry.duffy@exponential-e.com</RecipientAddress>
  <RecipientStatus>0</RecipientStatus>
  </Recipient>
  </Recipients>
  </Exchange_MessageTrackingEntry>
- <Exchange_MessageTrackingEntry>
  <TimeLogged>2006-11-1 10:05:22</TimeLogged>
  <OriginationTime>2006-11-1 10:05:22</OriginationTime>
  <KeyID>\\delta.Exponential-e.it\DELTA.log\20061101.log,5557771</KeyID>
  <MessageID>DD28797B4AA4C34BAFF5CBF96740815C0EEA78@delta.Exponential-e.it</MessageID>
  <ServerName>delta.Exponential-e.it</ServerName>
  <Subject>test</Subject>
  <EntryType>1019</EntryType>
  <RecipientCount>1</RecipientCount>
  <Priority>0</Priority>
  <Size>11337</Size>
- <Recipients>
- <Recipient>
  <RecipientAddress>carry.duffy@exponential-e.com</RecipientAddress>
  <RecipientStatus>0</RecipientStatus>
  </Recipient>
  </Recipients>
  </Exchange_MessageTrackingEntry>
- <Exchange_MessageTrackingEntry>
  <TimeLogged>2006-11-1 10:05:22</TimeLogged>
  <OriginationTime>2006-11-1 10:05:22</OriginationTime>
  <KeyID>\\delta.Exponential-e.it\DELTA.log\20061101.log,5557954</KeyID>
  <MessageID>DD28797B4AA4C34BAFF5CBF96740815C0EEA78@delta.Exponential-e.it</MessageID>
  <ServerName>delta.Exponential-e.it</ServerName>
  <Subject>test</Subject>
  <EntryType>1025</EntryType>
  <RecipientCount>1</RecipientCount>
  <Priority>0</Priority>
  <Size>11337</Size>
- <Recipients>
- <Recipient>
  <RecipientAddress>carry.duffy@exponential-e.com</RecipientAddress>
  <RecipientStatus>0</RecipientStatus>
  </Recipient>
  </Recipients>
  </Exchange_MessageTrackingEntry>
- <Exchange_MessageTrackingEntry>
  <TimeLogged>2006-11-1 10:05:22</TimeLogged>
  <OriginationTime>2006-11-1 10:05:22</OriginationTime>
  <KeyID>\\delta.Exponential-e.it\DELTA.log\20061101.log,5558137</KeyID>
  <MessageID>DD28797B4AA4C34BAFF5CBF96740815C0EEA78@delta.Exponential-e.it</MessageID>
  <ServerName>delta.Exponential-e.it</ServerName>
  <Subject>test</Subject>
  <EntryType>1024</EntryType>
  <RecipientCount>1</RecipientCount>
  <Priority>0</Priority>
  <Size>11337</Size>
- <Recipients>
- <Recipient>
  <RecipientAddress>carry.duffy@exponential-e.com</RecipientAddress>
  <RecipientStatus>0</RecipientStatus>
  </Recipient>
  </Recipients>
  </Exchange_MessageTrackingEntry>
- <Exchange_MessageTrackingEntry>
  <TimeLogged>2006-11-1 10:05:22</TimeLogged>
  <OriginationTime>2006-11-1 10:05:22</OriginationTime>
  <KeyID>\\delta.Exponential-e.it\DELTA.log\20061101.log,5558320</KeyID>
  <MessageID>DD28797B4AA4C34BAFF5CBF96740815C0EEA78@delta.Exponential-e.it</MessageID>
  <SenderAddress>ADEEL.AHMAD@Exponential-e.com</SenderAddress>
  <ServerName>delta.Exponential-e.it</ServerName>
  <Subject>test</Subject>
  <EntryType>1033</EntryType>
  <RecipientCount>1</RecipientCount>
  <Priority>0</Priority>
  <Size>11337</Size>
- <Recipients>
- <Recipient>
  <RecipientAddress>carry.duffy@exponential-e.com</RecipientAddress>
  <RecipientStatus>0</RecipientStatus>
  </Recipient>
  </Recipients>
  </Exchange_MessageTrackingEntry>
- <Exchange_MessageTrackingEntry>
  <TimeLogged>2006-11-1 10:05:22</TimeLogged>
  <OriginationTime>2006-11-1 10:05:22</OriginationTime>
  <KeyID>\\delta.Exponential-e.it\DELTA.log\20061101.log,5558531</KeyID>
  <MessageID>DD28797B4AA4C34BAFF5CBF96740815C0EEA78@delta.Exponential-e.it</MessageID>
  <SenderAddress>ADEEL.AHMAD@Exponential-e.com</SenderAddress>
  <ServerName>delta.Exponential-e.it</ServerName>
  <Subject>test</Subject>
  <EntryType>1030</EntryType>
  <RecipientCount>1</RecipientCount>
  <Priority>0</Priority>
  <Size>11337</Size>
- <Recipients>
- <Recipient>
  <RecipientAddress>carry.duffy@exponential-e.com</RecipientAddress>


Hope this is enough info for you to help me.  If you have any questions please do so.

Any help is appreciated.



Regards



Mbavisi