Notizbuch
It took me some hours to find the origin of the error, so I'll documentate some hints here for you. I am running postfix with postgresql on Debian. But it should apply more or less to MySQL and FreeBSD and other OS, too.
This card, named "Unlimited USB Modem AC885" by swisscom, is described to be unsupported in many forums, but that is not true.
In this post I describe what is needed to get it running with the Swisscom network in switzerland.
Imagine the following situation:
[You (dynamic IPN, somewhere travelling)] -> [your server] -> [gatewayserver] -> [trusted servers]
The only way to reach the trusted servers is through the gateway server, which again is only reachable from "your server".
To make life easy, ssh can easily manage this via the ProxyCommand.