Email question

I am running RT 3.4.5 straight from the box using Fedora Core 5, and I
have sendmail creating tickets

It appears to be running OK I can create and resolve tickets no problem.

However there is something I can’t figure out.

If I email a new ticket from localhost then a ticket gets created and a
reply sent back to confirm, and using the reply feature emails get sent
to the requestor.

If I email from another local machine the ticket gets created but no
cofirmation gets sent, and using the reply facility does not sendmail.

If I change the requestor on the ticket created above to another
external email address and then reply email is sent to the requestor
address. Both the addresses are on the same local mail server.

I am not quite sure where to start I have granted full rights to
everyone on the general queue to eliminate permission/rights issues.
Could someone kindly point me in the right direction.

Kind Regards

Neil Baldwin