.TH s/qmail: srsreverse 1
.SH NAME
srsreverse \- reconstruct the original address from its SRS extension 
and forward bounce mail
.SH SYNOPSIS
in
.BR .qmail :
.B |srsreverse
.SH DESCRIPTION
Upon reception by
.BR qmail-smtpd ,
.B qmail-local
may feed a locally delivered bounce email through
.B srsrevers
in order to reconstruct the original sender from
the received SRS address provided in the local part
and to forward the bounce mail to its original address.
.SH "SRS DOMAINS"
In order to accept emails for SRS modified
return addresses, you need to setup those in
.IR rcpthosts .
If your domain is
.I example.com
in
.I rcpthosts
you probably want to set up additionally
.IR srs.example.com .
However, 
.I .example.com
would be fine as well.
.SH "VIRTUAL SRS USER"
SRS can facilitate a virtual user typically named
.I srs
and thus requires an entry like
.I srs.example.com:srs 
in
.IR virtualdomains .
.SH "DOT QMAIL"
.B srsreverse
is called from a 
.I dot-qmail
file which could be
.IR SQMAIL/alias/.qmail-srs-default .
.SH "CONTROL FILES"
.B srsreverse
reads the control file 
.I virtualdomains
to exfiltrate the (virtual) SRS user name for the received domain, 
if given. With the evaluated
.IR srsdomain ,
.B srsrevers
fetches the
.I SRS secret
from 
.I srsdomains 
in order to validate the SRS bounce address.
.SH "ENVIRONMENT VARIABLES"
.B srsrverse 
reads the environment variables
.IR DTLINE ,
.IR HOST ,
and
.IR RECIPIENTS .
.I HOST 
is used to determine the 
.IR srsdomain .
The forwarding bounce address is reconstructed from
the local part of 
.IR RECIPIENTS .
.SH VERP
The Sender Rewriting Scheme SRS can be considered 
as tailored form of VERP: Variable Envelope Return Path. 
The chosen primary delimiter
.I =
is recognized by 
.BR qmail-smtpd 's
recipient extension.
.SH REFERENCE
.B srsreverse 
uses srs2.c from
.IR libsrs2 .
.SH "SEE ALSO"
srsforward(1),
dot-qmail(5),
qmail-command(8),
qmail-queue(8), 
qmail-send(8).