[Exim] $return_path problem

Hello everyone,

I want to set the Return-Path header during the final smtp transport
as described in chapter 48 (support VERP), but with no luck. Here is
how my config file looks like:

 remote_smtp:
        driver = smtp
        interface = a.b.c.d
        command_timeout = 1m
        connect_timeout = 5m
        return_path = \
                ${if eq {$return_path}{smth@???} \
                {smth-bounce=$local_part%$domain@???}fail}

when i inject mail into exim`s queue with a command like this:
exim -odqs -f smth@??? -bm address@???
and run exim -q i can not see that the Return-path header contains
what i want. It contains the smth@???. And even if i try to
send a message using SMTP still no luck. Any help will be great

---
return_path (transport)
Type: string, expanded
Default: unset

If this option is set, the string is expanded at transport time
and replaces the existing return path (envelope sender) value.
The expansion can refer to the existing value via $return_path.
If the expansion is forced to fail, no replacement occurs;
if it fails for another reason, Exim panics. This option can be used to
support VERP (Variable Envelope Return Paths) -- see chapter 48.
---

---
Best regards,
Alexei V. Alexandrov