Setup and configuration

[Henry]

Our public domain name is "mydomain.com.au" and our LAN internal
domain is "int.mydomain.com.au"

In Kolab all users use the domain name "int.mydomain.com.au" and I
have added "mydomain.com.au" as a domain alias.

This appears to work but is a bit clunky as the internal domain should
not be used for email.

I am also unsure of the purpose of the "External Email Address"
setting as each user will be receiving email under multiple domains
specified as aliases and each user will send email using the different
domain (setup as identities in RoundCube) so what should be entered
for the External Email address and how is this used?

Thanks