The whole connection depends on the session object, so if you want to change
the properties during runtime, you have to kill the connection
, make a new session object with the new Properties and reconnect .
If you use authenticator, you have to be reinit it also.

this line of code change my properties during runtime:

folder.close
store.close
authenticator = new Authenticator(properties);
session = getInstance(properies);
store.connect(..);
folder.open();


dont use the default instance when reconnecting.
this doesn't change the prop and session object. (this is not a good feature in javamail i think!)

hope this helps someone
Alex