[Dovecot] UTF-8 mailbox names in filesystem

[Ben Winslow]

On Mon, 09 Nov 2009 21:11:23 -0500
Timo Sirainen <tss at iki.fi> wrote:

> Currently mailbox names are stored in IMAP's modified-UTF-7 format in
> filesystem. I was wondering about changing this in v2.0. The default
> would still be to use mUTF-7 in filesystem, but just adding :UTF8 or
> something to mail_location could enable UTF-8.
> 
> Any thoughts? Could this be dangerous somehow? UTF-8 enables a lot of
> weird characters, perhaps no one really wants to see them on
> filesystem since there's no way to type the characters? But for small
> systems this probably isn't a problem.

A while ago, I was playing around with the idea of encoded '/'s in
Maildir names since many people have asked for a way to use them.
UTF-7 does not require that each character be representable in only 1
way like UTF-8 does, so it's possible to encode US-ASCII characters and
put them into the folder name; however, I found that most clients
decode any mUTF-7 in folder names while parsing LIST/LSUB replies and
then discard the name given by the server (expecting that they can just
re-encode any non-ASCII characters and still arrive at the correct
folder name.)  While I would argue that these clients are buggy, the
bug seems to be so common that encoding characters this way isn't
practical.  With that in mind, you do lose the ability to encode
characters like this if the folder names on disk are UTF8, but that's
not much of a loss anyway if UTF8 encoding is optional.

So far as UTF-8 on the filesystem is concerned, I've been using UTF-8
in filenames on my personal systems for years now without any real
issues.

-- 
Ben Winslow <rain at bluecherry.net>