For systems which automatically generate address lists for replies to messages, the following recommendations are made:
o The "Sender" field mailbox should be sent notices of any problems in transport or delivery of the originalm essages. If there is no "Sender" field, then the "From" field mailbox should be used.
o The "Sender" field mailbox should NEVER be used automatically, in a recipient's reply message.
o If the "Reply-To" field exists, then the reply should go to the addresses indicated in that field and not to the address(es) indicated in the "From" field.
But, not all mail servers obey this rule. Some mail servers will bounce it back to the FROM address.
Further reading:
The Internet Engineering Task Force (IETF) for Emails at http://tools.ietf.org/html/rfc822#section-4.4
Did you get any bounces to go to the FROM email address at all?
Hope this helps
Rajesh