maintain message threads

when you receive a message from somebody and you wish to reply to it, just reply to it.  don't create a new message on the same topic, it's confusing to both the recipient and to threaded mail readers.

conversely if you wish to create a new message thread, just create a new message with a fresh subject line.  don't dig around in your mail box for an old message from your intended recipient and reply to it.  it is confusing to receive a message out of the blue containing content completely unrelated to the subject line.

if you have a message thread going with one or more persons and you wish to talk about unrelated topics, go ahead and start another thread.  threads are context, and context is good.