Recipients are having problems replying to email with CC

Hi,

whenever I send an email outside of my Domino domain with someone in the CC field, the recipient will receive the email with the email address of the sender in the from field, but will have the Domino user in the CC field.

For example, if I send an email from Stephane Richard/Organisation and I put Joe Doe/Organisation in CC, the recipient will see in the from field stephaner@organisation.com, but will see Joe Doe/Organisation in the CC field.

It is obvious that if that recipient tries to reply to all to my email, he will get an non-delivery warning since it cannot resolve Joe Doe/Organisation.

What could I do and where could I look to fix this problem.

Thank you.