Strange email issue

I have an user, that occasionally when he sends out an email it is delivered to users that he did not intend it to go to.

For example he addresses the email to PersonA, and PersonB and latter finds it has been routed to PersonA, PersonB, and PersonC.

I have exported one of the messages and found that one of the “unintended” recipient’s address is listed in the INetSendTo field, but that same individual is not listed in the SendTo field of the message.

So it appears that somehow the INetSendTo field is being populated with a value it shouldn’t be.

Any thoughts of how this might be occuring would be greatly appreciated…

Thanks In Advance