Hi to all

I have a system so configured:

Mail Server 1 (Lotus Domino) -> Postfix -> ISP's SMTP

On postfix I implemented the "sender_dependent_relayhost_maps" setting for each user with an SMTP username and password.

The e-mails come from the server 1, go to postifix that manages the output based on the sender. Everything works.

In case of shared mailbox, when the user A opens the shared mailbox X, the mail is sent with the following header from the first server:
Sender: A
From: X
When postfix receives the email, the sender recognizes as A and uses the SMTP server A and not of X. This is a problem.

I tried to modify the header of the email before sending modifying or eliminating the Sender field, but any operation I do the email out anyway as if it had been sent by A and not by X.
On the postfix log I see pass email
From <A> to <external recipient>.

I can not use map "when sends A change it to B", many users open their mailbox and the same shared mailbox.

Some of you would know give me some suggestions on the way forward?