....That also provides the outbox for the account

The Smtp resource should provide:

• One Outbox folder, that is a subtype of a mailfolder
• An Outgoing mail message type, that has extra properties:
  • send strategy (with an enum value of NOW) for the time being
  • sent-folder
  • identity

The resource can store the mail in a configfile or so (anywhere on disk really), and then try to dispatch it immediately.
Any modification will trigger another try to send (in case it failed because of no network), and a sync triggers a new of all messages as well.

Not implemented are:

• query
• retry via modify
• retry via sync