[Dovecot] Subaddress Extension in sieve plugin

[Frank Behrens]

Hello!

With many MTAs it is possible to use a special form of adressing: subaddresses or "plussed 
addresses". For sendmail you can read some information on
http://www.sendmail.org/m4/misc_features.html
http://www.unix.org.ua/orelly/networking/sendmail/ch24_04.htm#SML2-CH-24-SECT-4-3

In a sieve filter you can analyse these special detail values, the syntax is described in 
RFC3598 (http://tools.ietf.org/html/rfc3598).

The current deliver with sieve plugin for dovecot seems to support this RFC, but has the 
detail information not available. If I use

require ["subaddress", "fileinto", "reject"];
require "envelope";
if envelope :detail "to" "junk" {
       fileinto "junk";
}

the rule is not triggered, because the detail information from envelope is not available. Deliver 
gets the user information only via command line switch "-d".

I did not analyse the problem very deep, but I believe we should introduce a new command 
line parameter for deliver, so deliver can pass the detail information to the sieve plugin. With 
that parameter you are able to pass the detail information from sendmail to devecot's deliver 
in the same way procmail is handled (procmail uses -a parameter).

To avoid confusion: deliver has already a parameter -m to specify a different mailbox. In the 
described case the mailbox should be determined by the sieve filter, not via command line 
parameter.

Existing workaround: Because I need this functionality I wrote a quick (and dirty?) 
workaround. Sendmail does not call deliver directly, but a wrapper program, that adds an 
additional "Delivered-To" header line. So the detail information may be processed with
       if address :detail ["Delivered-to"] "junk" {
but I would prefer to call deliver directly.

What do you think, is it a useful extension and does it work?

Regards,
   Frank
-- 
Frank Behrens, Osterwieck, Germany
PGP-key 0x5B7C47ED on public servers available.