The only thing that determines which SMTP server a user should use is their physical connection to the internet. For instance, if a user is connected to the internet through MyISP, Inc. then he or she must use MyISP's SMTP server, no matter what identity they will be sending mail with. The SMTP server list is accessable through the SMTP Service. Currently, you can set the default SMTP server to something else by setting the defaultServer property on the smtpService, but that will not be saved to disk. Eventually there will be the concept of a session default server, and a permenant default server.
All preferences are strings, unless otherwise noted.
The incoming server associated with this account. The list of identites associated with this account.