curious about some implementation issues

[Sergei Gerasenko <sergei@xxxxxxxxxxxxxxxxxxxxx>]

I've been curious about two things about mutt.

1) If I understand correctly, marking a message as "read" involves
inserting a "Status:RO" line into the header of the message. How does
mutt do that pricesely? I mean, is it modifying the file in place or
does it create a temporary file, which is then renamed? I've been
ignorant of this and similar problems (e.g. working with flat files) for
two long and it's about time I ask!

2) How does mutt make sure that while it's modifying the mailbox, the
delivery agent is not adding something to it at the same time?

Thanks for your time.

Sergei