Looks good - I would remove the requirement for setting text and html in order, as pr0gm4n and Stephen suggested (delay building until send, and cache it when built), but then clear that cache when the text or html properties are modified.
I'd also suggest that you allow sending text-only e-mails if the html property is left blank (you don't have to use multipart/alternative, plain text e-mails are in fact OK - it's HTML only e-mails that are bad).
Last bit would be that it appears at first glance as if your class will fail if the session.convertmime property isn't set correctly before you instantiate the class - that could be hard to track down if someone were just getting started in LS. That would make me want to build the body in the send routine, but might make caching it a bit difficult.
Looks good - I would remove the requirement for setting text and html in order, as pr0gm4n and Stephen suggested (delay building until send, and cache it when built), but then clear that cache when the text or html properties are modified.
I'd also suggest that you allow sending text-only e-mails if the html property is left blank (you don't have to use multipart/alternative, plain text e-mails are in fact OK - it's HTML only e-mails that are bad).
Last bit would be that it appears at first glance as if your class will fail if the session.convertmime property isn't set correctly before you instantiate the class - that could be hard to track down if someone were just getting started in LS. That would make me want to build the body in the send routine, but might make caching it a bit difficult.