Web Server migration for a near (April) End of Life server is in progress this morning. Some websites are being moved to a new virtual server and may be unavailable during the transition. No email services will be affected. If you notice that your site is still down by noon CST today, don't hesitate to contact us. The server upgrade is not only contains security updates, but also function updates which may affect your sites. I'll be checking each one cursorily, but a deep check (logging into your admin, etc) is impossible.
Although Mozilla Thunderbird may have a dated interface, it is a powerful and flexible email client. We use autoconfig on our DNS servers so that when you add your email address and password to the Account Settings, it should automatically find then add your settings auto-magically.
If this does not work, this is likely because your DNS servers are hosted elsewhere than the primary iThinc DNS servers and you'll need to set up the settings manually with the settings found on this page.