We have created a addin which will work for addtional server type storage. We
don't do any thing with Outlook email form . We have custom form which
handles the messages of our Message Store.

Problem Description
'A' is Exchange Server mailbox and 'B' is MyServer (additonal server type)
mailboxes are configured under same profile. B mailbox has some emails in its
inbox. Now if I try to reply to that email outlook takes Exchange Server as
its account whereas it is supposed to be MyServer Email account. Every time
while replying to the email in B mailbox I need to select MyServer account
using drop down.

I have tested this case with
1) IMAP4 and MyServer
2) POP3 and MyServer
It works fine with these combinations.

What can I do to work it properly for combination with Exchange?