Re: [9fans] gmail's new POP features + upas/fs

[Russ Cox <russcox@gmail.com>]

> The upas/fs pop3 code uses message numbers, not UIDs,
> to identify messages on the server, and expects that
> messages will be in the same order each time the client
> reconnects.  I found this expectation wasn't true with
> the demon.co.uk server, and indeed it doesn't seem to
> be stipulated anywhere in the RFCs.

Well, yes and no.  It does use the UIDs but also depends
on ordering.  It expects new messages to appear at the
end of the list, which isn't stipulated in the RFCs but has
been true of every POP3 server I've ever seen (except the
original Plan 9 one, but I fixed that).  At the time I wrote
the code, it seemed that there were enough other mail
readers expecting the oldest->newest sort order that
it seemed a safe assumption.  To be fair, nowhere in the
spec does it say that the server has to support UIDs either,
so there's not really a safe way to do the upas/fs 
"stay in sync with the server" trick.  

I don't think this is Gmail's problem.  If that were happening,
the messages would just look reordered.  I'm pretty sure
gmail remembers which messages the POP client has 
downloaded and never shows them to the client again.
This is kind of necessary to work around the fact that POP
doesn't scale so well.  Each time you connect you get the
next 300 messages you haven't downloaded yet.

Russ