Whenever you start actively checking a mailbox (i.e., not in
the background), and if there is a problem with a
connection, or the server is not responding, you click on
the Cancel button to stop checking, and nothing happens.
The program still tries to access the server. There is no way
to check another mailbox during this time. The program
does stop checking after some time, a minute or so. It
would be nice to be able to immediately stop the checking