Thanks for all the developers for K-9. I should have complimented them in my first message yesterday.
John, thank you for responding.
I will test your idea for the next days, but I think that there is at least two points in it that makes it sub-optimal:
1. you generate a notification whenever you send a message, which is annoying.
2. a thread which was created from messages exchanged while you were using GMail in the computer would not show all messages on the phone unless you send your messages with bcc on the computer also, which forces you to remember to do that for every message.
Nelson