eM Client is an email client with full support for all email and calendar services currently on the market, making it a great Thunderbird alternative. That includes native support for Gmail and Exchange accounts which you can set up in just a few seconds.
If you are looking for a full-featured email client which is still in active development, eM Client is the ideal solution. Migrating from Thunderbird is a matter of moments using the native import of your data into eM Client.