[exim] Problems with vacation message

With the following configuration that I have in the file exim.conf:

-----ROUTERS -----------
userforward:
driver = redirect
condition = ${if eq {}{${lookup ldap
{ldap://x.x.x.x/ou=xxxx,dc=xxxx,dc=xx?mailMessageStore?sub?(&(|(mail=${l
ocal_part}@${domain})(mailAlternateAddress=${local_part}@${domain}))(obj
ectclass=person))}}}{no}{yes
<mailto:mail=${local_part}@${domain})(mailAlternateAddress=${local_part}
@${domain}))(objectclass=person))}}}{no}{yes> }}
user = vmail
group = vmail
file = ${lookup ldap
{ldap://x.x.x.x/ou=xxxx,dc=xxxx,dc=xx?mailMessageStore?sub?(|(mail=${loc
al_part}@${domain})(mailAlternateAddress=${local_part}@${domain
<mailto:mail=${local_part}@${domain})(mailAlternateAddress=${local_part}
@${domain> }))} {$value} fail }/Maildir/forward
retry_use_local_part
no_verify
no_expn
check_ancestor
allow_filter
directory_transport = userforward_delivery
file_transport = userforward_delivery
pipe_transport = address_pipe
reply_transport = address_reply
ignore_enotdir
sieve_vacation_directory = ${lookup ldap
{ldap://x.x.x.x/ou=xxxx,dc=xxxx,dc=xx?mailMessageStore?sub?(|(mail=${loc
al_part}@${domain})(mailAlternateAddress=${local_part}@${domain
<mailto:mail=${local_part}@${domain})(mailAlternateAddress=${local_part}
@${domain> }))} {$value} fail }/Maildir/


----TRANSPORTS--------

userforward_delivery:
driver = appendfile
maildir_format = true
directory = ${sg
{$address_file}{(^[Ii][Nn][Bb][Oo][Xx])(.*)\/*}{${lookup ldap
{ldap://x.x.x.x/ou=xxxx,dc=xxxx,dc=xx?mailMessageStore?sub?(|(mail=${loc
al_part}@${domain})(mailAlternateAddress=${local_part}@${domain}))}{$val
ue} fail}/Maildir/\$2/}}
create_directory = true
delivery_date_add
envelope_to_add
return_path_add
user = vmail
group = vmail
maildir_tag = ,S=$message_size
directory_mode = 0700
mode = 0660


address_reply:
driver = autoreply

It happens to me, that when sending a mail to a user who has the
vacation filter activated, the mail that the sender receives back has
vmail@??? as from: header. But what we really need is
that this sender was the original message sender, not vmail.

Any ideas about how to change this fact? Or maybe it has to do with
rewriting that header in the vacation message?

Thanks in advance


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