Postfix - Howto prevent spoofing of local enmail address by sasl users?

I'm trying to setup remote access using sasl, so that users can send/receive mail remotely using
Outlook. At present they only have webmail access.

I'm using smtpd_sender_login_maps to prevent them sending mail with anything other than their
authorised email address. This works fine if they are sending email to an offsite address, however
they appear to be able to use any "from" address they like if they are sending mail to a user in the
local domain.

How can I prevent them from doing this, i.e. restrict their from address to what's coded in
/etc/postfix/smtpd_sender_login_map regardless of whether they are sending to a local or remote
user.

Extract from my main.cf below:

-------------------------------------------------------------------------------------------

#
# Enable sasl authentication
smtpd_sasl_auth_enable = yes
smtpd_sasl_local_domain =
broken_sasl_auth_clients = yes

#
# Restrict who can relay email via us
#
# 1) Users logged in remotely via SASL
#
# 2) Users local to mgw.org.uk (e.g. Webmail)
#
smtpd_recipient_restrictions =
permit_mynetworks,
permit_sasl_authenticated,
reject_unauth_destination

#
# Sender Restrictions
#
# 1) If logged in via SASL can only send mail from the address(s)
# registered to the user in smtpd_sender_login_maps
#
# 2) Any users on the mgw.org.uk subnet can do what they like.
#
smtpd_sender_login_maps = hash:/etc/postfix/smtpd_sender_login_map
smtpd_sender_restrictions =
hash:/etc/postfix/access,
permit_mynetworks,
reject_sender_login_mismatch

-------------------------------------------------------------------------------------------

Regards,
Martin

Martin White wrote:

>
> I'm trying to setup remote access using sasl, so that users can
> send/receive mail remotely using Outlook. At present they only have
> webmail access.
>
> I'm using smtpd_sender_login_maps to prevent them sending mail with
> anything other than their authorised email address. This works fine if
> they are sending email to an offsite address, however they appear to be
> able to use any "from" address they like if they are sending mail to a
> user in the local domain.
>
> How can I prevent them from doing this, i.e. restrict their from address
> to what's coded in /etc/postfix/smtpd_sender_login_map regardless of
> whether they are sending to a local or remote user.
>
> Extract from my main.cf below:
>
>
-------------------------------------------------------------------------------------------
>
> #
> # Enable sasl authentication
> smtpd_sasl_auth_enable = yes
> smtpd_sasl_local_domain =
> broken_sasl_auth_clients = yes
>
> #
> # Restrict who can relay email via us
> #
> # 1) Users logged in remotely via SASL
> #
> # 2) Users local to mgw.org.uk (e.g. Webmail)
> #
> smtpd_recipient_restrictions =
> permit_mynetworks,
> permit_sasl_authenticated,
> reject_unauth_destination
>
> #
> # Sender Restrictions
> #
> # 1) If logged in via SASL can only send mail from the address(s)
> # registered to the user in smtpd_sender_login_maps
> #
> # 2) Any users on the mgw.org.uk subnet can do what they like.
> #
> smtpd_sender_login_maps = hash:/etc/postfix/smtpd_sender_login_map
> smtpd_sender_restrictions =
> hash:/etc/postfix/access,
> permit_mynetworks,
> reject_sender_login_mismatch
>
>
-------------------------------------------------------------------------------------------
>
> Regards,
> Martin
....
Look at "sender_login_mismatch"...