easy:SetOpt_SASL_AuthZID(authzid)
When not specified only the authentication identity as
specified by the username will be sent to the server, along with the
password. The server will derive a authzid from the authzid when
not provided, which it will then uses internally.
When the authzid is specified, the use of which is server dependent, it
can be used to access another user's inbox, that the user has been granted
access to, or a shared mailbox for example.