[exim] Using exim over a GPRS connection

Hello,

I know that this question was subject on this list before but afaik
never really answered... So I will try again:

I have exim 4.44 with TLS support install on our mail server. Sending
mail via this server works fine from a PDA unsing a WLAN connection.
Were the is no AP near I want to use a GPRS connection. The client again
can connect to the server but the authentication seems not to work. The
mail is not "accepted" and gets rejected at the "dey" part of the ACL.
Again: it is the same client and the same configuration only the way how
to connect to the Internet (GPRS vs. WLAN) changes.

Any idea whats the problem here?

Any help would be very appreciated!

Regards, Jan