Firewall Wizards mailing list archives

Re: i-cap proposals


From: Carson Gaspar <carson () taltos org>
Date: Tue, 15 Feb 2005 02:08:59 -0500

--On Sunday, February 13, 2005 12:10 PM +0300 ArkanoiD <ark () eltex net> wrote:

Yes, IMAP is a content inspection nightmare - it was really insane to
deisgn it the way each one of zillion ways to get an email sliced to
little pieces and sucked down is mandatory to be implemented on server
and, thus, on the proxy!

No, it makes perfect sense. And it's why IMAP4 is the only mail client protocol that behaves well on low bandwidth links (and can be safely taken offline and re-sync'd). POP3 is the insane mail protocol. But I admit that proxying and scanning the content is much easier with stupid protocols.

You really should be doing scanning on the server. If you don't control the server, why are you allowing people to access it? If you insist on doing in-line scanning between the server and client, one option is to keep state on which messages have already been scanned during this session (pay attention to UIDVALIDITY). If any part (or any body part - see below) of a message which hasn't been scanned is fetched, do a full fetch in the proxy and scan it. If you trigger a scan on a header fetch, the user experience will suck, since most IMAP clients fetch from, date, and subject headers for a large subset of messages to display the mailbox summary.

--
Carson

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