i'll try to explain the best i can.
So i have an internal mailsever for family and friends with a couple of domains.
the internal mailserver and mail domains are protected via the UTM 9 SMTP proxy.
I have a small /29 IP V4 ip range for SSL , Mail and Web so those servers have a singel IPv4 address.
The problem is, if someone is extern and try to send mail via whatever iphone, laptop u name it, the SMTP proxy takes the connection and deny's it.
the only thing i get this working ist via Allow authenticated relaying in the relay Tab .
Edit: The SMTP Proxy does not run in transparent mode
But i think that is not the best solution, because i get a huhge amount of connection testing because of the open authenticated relaying.
Any hints ?
my suggestion is, use a (SSL) VPN to connect your external mail clients to the internal mail server.
BERGMANN engineering & consulting GmbH, Wien/Austria