Emails Delivered to Wrong Account

[Soulless]

I am running Small Business Server 2000 with Exchange 2000. I run no spam filters or anything like that.
Last month a strange problem started occuring. Every now and again emails would be sent to A@mydomian.com, but would be delivered to B@mydomain.com mailbox.
No rules have been setup to make this happen either on the server or on the clients, and its only happens on odd occasions.
When it does happen the email turns up in B's inbox, but the "To" address clearly states A.
Does anyone have any ideas because so far I am totally stuck.
Thanks in advance.

 

[Davetoo]

The sender used a BCC to user B.

I'm Certifiable, not certified.
It just means my answers are from experience, not a book.

 

[Soulless]

Nope, there was no BCC used.
When the email gets delivered to the wrong account, if it was sent to user A, but gets delivered to user B, user A does not recieve any copy of the email at all.

 

[Davetoo]

Examine the mail headers further.

I'm Certifiable, not certified.
It just means my answers are from experience, not a book.

 

[Soulless]

I have looked into the mail headers but cant see any reason why it should be happening.
Is there anything in particular I should be looking for?

 

[Davetoo]

Verify that the header "To" is indeed A. Also, examine the emails that are exhibiting this strange behavior to look for a pattern.

I'm Certifiable, not certified.
It just means my answers are from experience, not a book.

 

[Soulless]

Ok the in the mail headers the To field is definitely correct.
I have looked for similarities but they dont seem to be any. The emails dont have a similar source and are routed through different paths.