[Dovecot] RFE: please add Return-Path: to sieve sent mail headers

May I ask to add Return-Path: some meaningful header line to sieve sent mail headers in vacation message? Now the header line isn't generated at all and the effect is as follows:

on receiving MTA:

2014-05-09T15:04:32+02:00 host/ip postfix/qmgr[2408]: 41F2F6024E: from=<>, size=900, nrcpt=1 (queue active)

in received mail body:

Return-Path: <>

Would be nice to get:

Return-Path: <user@domain>

Copy of From: header line could be sufficient.

Thanks.

MU