Hi Olivier,
Problem: some customers online via gprs are unable to send mails over these servers, because their external visible IP adress (gprs01.swisscom-mobile.ch: 193.247.250.1) is blacklisted on several lists:
I agree with Rene Luria: SMTP-Auth should always override dns-rbls.
A Swisscom GPRS-Customer is like eg. an ADSL-'dialup' (..dynip) customer: Such a client has absolutely no reason to connect to a 'foreign' (non-swisscom) Mailserver *without* using SMTP-Auth.
General question: are you (the postmasters around) using blacklists like dsbl or spamhaus directely on smtp-level (directely rejecting the mails from listed IP's) or only after (like in spamassassin & co.) ?
Bluewin rejects clients listed on xbl-sbl.spamhaus.org at SMTP-Level (but with a 'soft' error: 451)
-- Adrian