Enable sender handling for Exchange Accounts
* src/mail.cpp (Mail::update_sender): New. Updates sender address from OOM. (Mail::get_sender): New. Access the sender. (Mail::do_crypt): Pass sender to crypto functions. * src/mail.h: Update accordingly. * src/mailitem-events.cpp (EVENT_SINK_INVOKE): Update sender on send event. * src/message.cpp, src/message.h, src/mimemaker.c, src/mimemaker.h: Add optional sender parameter to crypto functions and use it.
In the after write event we can't use OOM methods so we can't look
up the sender over the session. This makes it neccessary to save
the sender address beforehand as I could not find any way to get this
information through MAPI (probably over the MAPISession).