Remote access to Horde Ingo

I’m trying to connect to a Sieve filter in Dovecot being part of a NS7 mail server.
If I telnet to port 4190 locally, I get “SASL” “PLAIN LOGIN GSSAPI”.
But if I telnet to port 4190 from remote, I get “SASL” “GSSAPI”.
Since I need PLAIN from remote I cannot connect.
Does anybody know the switch to change this restriction?