external mail from local user

[Corne]

I need to get kolab to accept mail from local users ie. user at domain.com
connected via modem dialup outside the lan sending to user2 at domain.com
on server kolab.domain.com.

I have gone through the amavis, postfix and spamassassin config looking
for a setting which could be changed to allow this but to no avail.

Any suggestions as to were I can look or read up on this  

TIA
Corne