Changes have been made in Git (master):

commit fb3da2a34b23e7d025b320641dbc85348a955cd3
Author: Jan Schneider <jan@horde.org>
Date:   Sun Nov 13 22:00:11 2011 +0100

     [jan] Set Return-Path: in Maildrop vacation driver 
(rsalmon@mbpgroup.com, Bug #10568).

  ingo/docs/CHANGES                   |    2 ++
  ingo/lib/Script/Maildrop/Recipe.php |    5 +++--
  ingo/package.xml                    |    2 +-
  3 files changed, 6 insertions(+), 3 deletions(-)

http://git.horde.org/horde-git/-/commit/fb3da2a34b23e7d025b320641dbc85348a955cd3

Changes have been made in Git for this ticket:

[jan] Set Return-Path: in Maildrop vacation driver 
(rsalmon@mbpgroup.com, Bug #10568).

  3 files changed, 11 insertions(+), 4 deletions(-)
http://git.horde.org/horde-git/-/commit/d262ca8d14e47986a75e46159704681185414307

Ah, I see what you meant now in your last comment.

with the following code, "-f" is an argument for sendmail, not mailbot :

'| mailbot %s -D %d -c \'UTF-8\' -t $HOME/vacation.msg -d 
$HOME/vacation -A %s -s %s /usr/sbin/sendmail -t -f %s'

What does sendmail have to do with this? You are patching the 
*mailbot* command invocation.

mailbot set 'From: ' and 'To: ' header properly, but not 'Return-Path: '

Assuming that files are owned by unix user 'vmail'
- with "/usr/sbin/sendmail -t" -> "Return-Path: <vmail@mbpgroup.com>"
- with "/usr/sbin/sendmail -t -f ''" -> "Return-Path: 
<MAILER-DAEMON@mbpgroup.com>"
- with "/usr/sbin/sendmail -t -f 'ronan@mbpgroup.com'" -> 
"Return-Path: <ronan@mbpgroup.com>"


I'm just after realising that we use virtual mail accounts which is 
probably why we are having this issue. Without the patch, sendmail 
sets Return-Path to the unix owner of the virtual mail accounts.

That doesn't look right. This is what mailbot's man page says:

        -faddress
            Address the autoresponse to address, which must be an RFC 2822[1]
            address. By default mailbot takes the autoresponse address from the
            From: (or the Reply-To:) header in the original message.  -f, if
            present, overrides and explicitly sets the autoresponse address.
            "address" must immediately follow the -f option without an
            intervening space (it´s a single command line argument). An -f
            option without an address takes the address from the SENDER
            environment variable.

So this is setting the vacation message's *recipient* but you set it 
to the user's From address.

return-path is not set to the right user


the attached patch properly set the 'Return-Path' variable in the 
message header.