TRY_NULL_MX_LIST

[Marc]

Hi there,

Can someone explain me the purpose of TRY_NULL_MX_LIST ? I read the
README but don't quite understand for what it's really usefull for.

Thanks

Regards

[Neil W Rickert]

Marc <syn_uw@NOSPAM_hotmail.com> writes:

>Can someone explain me the purpose of TRY_NULL_MX_LIST ? I read the
>README but don't quite understand for what it's really usefull for.

You firewall your network.

For all internal hosts, you set an MX record pointing to
your firewall gateway machine.

Mail comes to the gateway machine. When it lookups up the MX
records, it deletes the MX record pointing to itself and anything
with worse precedence. This leaves the MX list empty (null).

Because of the `TRY_NULL_MX_LIST' configuration, sendmail now
looks up the IP address and sends directly to that. Since it
is your gateway machine and has access to internal hosts,
this succeeds.

Without `TRY_NULL_MX_LIST' you would need to setup a mailertable
to work around what the MX records show. This eliminates that
step.

(Note: It is probably better to setup the mailertable anyway, for
more precise control).