Due to the rise of web-based mail, there aren't as many choices as previously.
I still use Thunderbird from Mozilla.org without any issues at all. I'm using an old version (3.1.7) and don't know if newer versions are better or worse.
My Computer
Computer type
PC/Desktop
Computer Manufacturer/Model Number
Ignatz Special; 4 speed manual gearbox; factory air conditioning; one of one
OS
Windows 7 Home Premium SP1, 64-bit
CPU
Intel Skylake i5-6600K, not overclocked
Motherboard
AsRock Z170M Extreme 4, micro ATX
Memory
8 GB HyperX DDR4-2666 (2 x 4 GB)
Graphics Card(s)
none; graphics are integrated on CPU
Sound Card
onboard: Realtek ALC1150; external: USB Behringer UF0-202
Monitor(s) Displays
Dell S2340M 23 inch IPS
Screen Resolution
1600 x 900
Hard Drives
System: Crucial MX100 series SSD, 128 GB;
Data: Samsung Spinpoint 103SJ, 1 TB;
Backup: WD Caviar Green WD30EZRX-00D8PB0, 3 TB
Microsoft Security Essentials and Malwarebytes Premium
Browser
Pale Moon
Other Info
All fans PWM; speeds at idle: CPU circa 500 rpm; intake circa 600 rpm; exhaust circa 600 rpm; CPU temps 27 idle and 47 C load in a warm room (27 C/81 F) when running Intel Extreme Tuning Utility stress test.
2nd ASUS X299 Apex/Intel i9-9940x with Custom water loop/7H-Prem-x64/Corsair 450D case/Ram Trident-z 3600C16 4x8gb / Samsung970Evo plus 500gb SSD/Dual ssd EZ swap evo/PSU EVGA SuperNova 1200w-P2 80+Platinum/GPU Titan Xp /8-ML-140 on push-pull on 2-280GTX rads