Tickets :: Comment on [#8922] Sort messages by arrival date not working correctly

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Comment	>> But why would users be interested in IMAP servers internal info like >> message sequence number/UID? > > Because it is the fastest sort. All IMAP servers necessarily need to > track their message sequence numbers, so sorting by this value is > "free" (as opposed to date sort - this requires each message's header > to be parsed to get the date value). > >> Looking at the IMAP SORT RFC >> (http://www.faqs.org/rfcs/rfc5256.html) I found the ARRIVAL sort type: >> >> ARRIVAL >> Internal date and time of the message. This differs from the >> ON criteria in SEARCH, which uses just the internal date. > > Yes. ARRIVAL SORT = message sequence number. This statement is > nothing more than providing a keyword to use for SORT to do the same > thing as a regular arrival sort. > >> And this is exactly what gets called if I disable the IMP _arrival >> cache. So _arrival cache pretends to implement this IMAP search type >> but does something different - sorts on UID instead of IMAP internal >> date. As a result our users see messages that are almost randomly >> sorted. The worst thing is that arrival sort type is the default. > > _arrival cache does not to "pretend to implement this IMAP search > type". The arrival cache implements a cache of the message sequence > numbers. > > Arrival sort is on by default because it is the only sort that can > reasonably be used on large mailboxes on ALL IMAP servers. > > Unfortunately, you are assuming a lot of things about IMAP servers. > First, the SORT extension wasn't standardized until June 2008. So > there can be no assumption that the IMAP server supports SORT (not to > mention IMP 4 was first released 5-6 years ago, before SORT existed > on most IMAP servers). > > Second, many IMAP servers don't support SORT. It's not required of > an IMAP 4rev1 server. Thus, to sort by anything other than internal > arrival time requires the IMAP server to parse EVERY header of > EVERY message in the mailbox (a MUA can use FETCH to only return > the text of the desired header, but this still requires the IMAP > server to internally parse every header to collate this information). > > Third, even for IMAP servers that support SORT, there is no guarantee > that SORT is inexpensive. Many IMAP servers may not cache this > information, so every SORT call to the server requires parsing of the > entire mailbox. > > The issue with sorting a mailbox, at least with the original IMAP > 4rev1 spec, is that IMAP was originally designed to act in a > connected environment. Meaning that you logged on once in the > morning and your e-mail client handled issues like sorting ONCE > (since further changes could be caught via untagged responses since > the IMAP client was always connected to the IMAP server). IMAP was > NOT designed for disconnected clients, such as webmail, that were > constantly connecting/disconnecting from the server. Tools have > slowly been developed to help this situation (imapproxy, RFC > extensions, webmail server caching) but usage of these tools can not > be guaranteed in any single installation. > > Thus, the only reasonable default sort is ARRIVAL.
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