Hi,
i changed a user account e-mail adress using the admin panel.
Now, each e-mail sent by this user is very strange :
the "Sent by" field contains his new e-mail adress
BUT
there is a "On behalf of" field which contains the old e-mail adress
And then when a recipient try to reply to this user, the reply adress is the old adress, which no longuer exists !!!