Thunderbird broke - need new mail client

[mahesh]

As the title says. After autoupgrading to v115.2, the unified folder is broken and throws errors. And there are several other small quirks in the UI that just do not seem right(buttons missing, addons disabled, etc). After browsing for help on the subject there is a LOT of posts asking for help, but no solutions to for a majority of the problems with this upgrade.
I need a client that can handle multiple accounts and have a unified folder. It would be nice to import my calendar and contacts to the new mail client.
What do you suggest?
Laptop - Lenovo-IdeaPad-S340-15IWL,i3-8145U CPU @ 2.10GHz, 8GB DDR4, 256GB SSD , 20.04 Linux Mint
Desktop - Lenovo ThinkCentre M81 Intel Core i7--2600 3.8GHz, 8GB DDR3 Samsung SSD 850 EVO 500GB, 16.04 64bi