Read message has been changed. Virus?

[Richard]

A few days ago, I sent one of my customers an email. He replied to me the
same day. Today, I got another message from him & when I opened it, it
looked like a simple return receipt, but when I went back to look at his
reply from a few days ago, it had been changed. His reply text was gone & it
now just had my original message in it. The 'from' text also showed
(e-mail address removed) for (e-mail address removed) (his email address for his email address)

Is this perhaps some sort of virus, or is there some way that this guy was
able to change his reply that he sent me a couple days ago? I know Outlook
has a tool that allows you to retrieve a message that you sent by mistake, as
long as the recipient hasn't opened it yet, but is there also a tool to allow
you to amend an email, even after the recipient has read it?

FYI, I'm using Outlook 2000 SP-3

Any help would be appreciated

 

[Marvin P. Winterbottom]

In the two messages, go View/Options and look at the internet headers. This
tells you where the email really came from. Are they the same? If not, the
second one is probably a virus. A virus can put any address it wants in the
FROM field.

 

[Richard]

Nothing looked out of the ordinary. An addendum....the 'from' email
addresses read "(e-mail address removed) on behalf of (e-mail address removed)" where both
addresses were the same, and were from the person I sent the original message.