Hi guys,
In our latest release, we added a feature that might help fight against these attacks. Each domain now has an option in Domain Settings > General for 'Block Authentication by Country'.
This feature will allow you to block authentication attempts from specific countries, or ONLY ALLOW authentication from specific countries. Adding a country to the setting will just block authentication attempts, it won’t impact sending or receiving messages from the country. It will simply prevent anyone from the excluded countries from logging into the server, regardless of protocol.
I hope this helps!
Andrea Free
SmarterTools Inc.
877-357-6278
www.smartertools.com