--Same setup works fine with Exchange 2003
--But it is not possible to connect to Exchange 2010
--Error:
connection established. +OK The Microsoft Exchange POP3 service is ready..
C: USER france\gateway.
S: -ERR Command is not valid in this state..
login refused. -ERR Command is not valid in this state..

By default Exchange 2010 is configured to request SSL.

1. Disable SSL on the Exchange Server side
or
2. Enable SSL on Gateway side