For example, you maybe publishing OWA via an external IP on your Sophos UTM, your users can no longer connect to OWA when on mobile phones, but can from any other site, it maybe that the mobile providers IP address has been blacklisted.
So you may see the following error’s in the Sophos UTM logs, this will usually show in the reverseproxy.log: file :-
Client is listed on DNSRBL black.rbl.ctipd.astaro.local
This means that the client IP appears on a blacklist, this shows in the log as the “srcip” field. Sophos uses the Cyren database, you can check your IP address at the following URL :-
From that page you can also request the blacklisted IP address to be removed, however this should be for the provider to do.