Date: Tue, 12 Jan 2010 11:19:09 +1300
From: martin f krafft <madduck@madduck.net>
To: mailtags discussion list <mailtags@lists.madduck.net>
Message-ID: <20100111221909.GA30299@lapse.rw.madduck.net>
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Cc: notmuch discussion list <notmuch@notmuchmail.org>
Subject: [notmuch] Idea for storing tags
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Folks, over in #notmuch, we just floated an idea that I'd like to
get out to you. We've been debating storing tags for messages.
Therefore I am cross-posting. Please forgive me.

So far, there are two approaches:

1. External database, which has the downside of not being
   synchronisable with standard IMAP, like the rest of your mail
   (assuming you use IMAP). Also, it's possible for mailstore and
   database to get out of sync.

2. In-headers, which has the downside of leaking (e.g. when
   bouncing), and incurs the risks associated with message rewrites
   (which I think is pretty much ignorable, but it's still there).
   Also, there's a performance issue, but in the context of an
   indexer like notmuch, this is negligible.

   The leakage is real, though and I think it makes in-headers
   unusable. After all, I don't ever want anyone else to know that
   I tag e-mails from my boss as "from-idiots", and I forward and
   bounce mail on a regular basis. I could tell my MTA to remove
   those headers, but I might forget to do that on a new system.

We also previously determined that IMAP keywords are pretty much
useless as they are stored per mailbox, not per message, not
standardised, and limited in their length anyway [0]. This also
means that we don't really need to investigate sensibly storing tags
in Maildir (e.g. with xattrs), because IMAP cannot transport them.

0. http://lists.madduck.net/pipermail/mailtags/2007-August/msg00016.html

Seriously, who implemented IMAPv4rev1 and what sort of crack were
they smoking??

I remember there was some KDE groupware contacts manager that used
IMAP to synchronise contacts. At first, this sounds horrible, but
when you detach IMAP from RFC822, it becomes a generic synchronising
protocol. The next step is then straight forward, and I want to
share this idea with you:

How about using pseudo-mails stored in Maildir and synchronised by
IMAP? E.g. every folder could have a subfolder .TAGS and if we find
a way to smartly pair messages between parent and subfolder, we'd
have a tag store alongside the mailstore it refers to, but without
the danger of leakage, and without having to rewrite messages.

The major problem with this is when clients don't understand this
"protocol", for then they will display all .TAGS folders as regular
IMAP folders, and try to treat the messages therein as regular
mails. Somewhere sometime this is bound to blow up and I don't
really know how to prevent that.

Anyway, the idea is out now. Thoughts?

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