Um, that's not what the OP asked for:
When I receive a message sent to one of my addresses: |
Reply from the same address the message was sent to
By default this is what BIS does if you have "properly" (i.e. use BIS the way it's designed to be used) integrated your email accounts.
I suspect that the OP probably has multiple accounts forwarded (or the addresses are aliases) to one account and that the one account is integrated with BIS?
Email account 1 ----\
Email account 2 ---------> Gmail -----> BIS
Email account 3 ----/
If that's the case then there's no way that BIS can properly handle things. The mail in my crappy ASCII art example comes from gmail to BIS and BIS will send all replies via gmail.
For what the OP desires each email account needs to be directly integrated with BIS.
Email account 1 ---------> BIS
Email account 2 ---------> BIS
Email account 3 ---------> BIS
Gmail -------------------> BIS
With this arrangement a reply will be sent by BIS using the account that the email message came from.
The caveat is that the OP will have to undo whatever was set up to forward mail from the multiple addresses to gmail (or set up filters in BIS) or else there will obviously be dupes.