Mailbird is an excellent freemium email client. It is equipped with several features, such as multi-account support, a handy task manager, and an integrated calendar. Mailbird, as of now, is Windows-only. Unfortunately, Mailbird for Mac OS has not yet been released. However, there are various alternatives available that you can use for Mac.
Thunderbird is a free email application that can be configured easily. You can also customize Thunderbird quickly. It has got some amazing features and these make it one of the best alternatives for your Mac computer.