Outlook 2003 reply to address issue

[JT]

Our CIO here has Outlook 2003 on his PC, every time he
clicks reply from a certian sender, the reply to address
that is supposed to have an underscore in it but removes
that underscore.

On other email addresses with underscores this does not
happen.

If you double click on the address from the received
message the reply to address is correct with the
underscore, however once you click on reply then again
double click on the reply to address it now shows without
an underscore.

I can't for the life of me figure this one out and our
CIO seems to be very bothered by this issue.

Any suggestions?

Thanks.