[Dovecot] Sieve/pigeonhole with Exim and Dovecot LDA

[Sebastian Arcus]

I am trying to configure my Dovecot installation to provide 
Vacation/Out-of-the-office emails using the Sieve plugin. My setup is a 
little bit peculiar:


     Internet                           Internet
        |                                  ^
        V                                  |
   Provider's POP3 server         Provider's SMTP server
        |                                  ^
        V                                  |    --------------
     getmail                               |     my server
        |                                  |
        V                                  |
   Dovecot LDA ---> Sieve/vacation -----> Exim
        |
        V
     Dovecot                                     my server
                                               ---------------


Sorry for the ASCII art above - I thought it would be quicker than 
trying to explain.

The trouble I'm having is getting the Dovecot LDA to send successfully 
through the local exim instance out-of-office replies back to the 
provider's smtp server - when receiving fresh email from the provider 
(through getmail). Dovecot LDA tries to send the replies - but Exim 
freezes them because they don't contain the sender data in the format 
Exim wants it. Exim can either receive sender info:

1. On the command line, after the "-f" command line switch (but only 
when called by root or other users passed under "trusted_users" in 
exim.conf).
2. In the header of the email - in the "From:" field - but only, 
apparently, if it was called with the "-t" switch. Full exim command 
line documentation here: 
http://www.exim.org/exim-html-current/doc/html/spec_html/ch-the_exim_command_line.html

I can't figure out what command line options the Dovecot LDA is using 
when calling exim. I also couldn't find a way to get Dovecot LDA to pass 
extra options to exim, when trying to send email. The exim log has the 
following:

2013-05-20 15:35:15 1UeRBB-0001xc-Ar Frozen (message created with -f <>)

I've inspected the frozen message - and it has the correct sender in the 
"From:" field - but it seems that exim isn't using that, because it 
wasn't called with the "-t" option.

In dovecot.conf, I have the following for Dovecot LDA and sieve:

protocols = imap sieve

protocol lda {
   log_path = /var/log/dovecot/dovecot-deliver.log
   info_log_path = /var/log/dovecot/dovecot-deliver-info.log
   postmaster_address = admin at mydomain.co.uk
   hostname = mydomain.co.uk
   mail_plugins = sieve
   mail_plugin_dir = /usr/lib/dovecot
   sendmail_path = /usr/sbin/exim
}

service managesieve-login {
    inet_listener sieve {
      port = 4190
    }
}

plugin {
    sieve = ~/.dovecot.sieve
    sieve_dir = ~/sieve
}

Dovecot LDA is called by getmail using the vmail user - and using the 
same user it is trying to call exim to deliver the out-of-office replies.

I'm using Dovecot 2.2.1 with pigeonhole 0.4.0.

I can post the rest of dovecot.conf if it would help. I've read through 
the stuff at dovecot.org - but all the Dovecot LDA and exim info refers 
to Exim passing email to Dovecot using Dovecot LDA - not Dovecot LDA 
sending email out using Exim.