Thunderbird is also available for macOS and should work fine.
I am a new Macbook Pro user. I bought a Macbook Pro 1.1 with MacOS
10.6.8 on 2020.11.18, and for some reason, I cannot open the Mail
program. There are no error messages, the program simply does not
want to open. I tried to look for alternative e-mail clients, but
they are all paid programs. I am looking for a simple, good, free
e-mail client for Mac OS X 10.6.8.

 Web-based telnet client
Web-based telnet client Telnet
Telnet RLogin
RLogin IRC
IRC Email & news access
Email & news access| Sysop: | Eric Oulashin | 
|---|---|
| Location: | Beaverton, Oregon, USA | 
| Users: | 102 | 
| Nodes: | 16 (0 / 16) | 
| Uptime: | 09:11:31 | 
| Calls: | 7,039 | 
| Calls today: | 4 | 
| Files: | 8,559 | 
| D/L today: | 1,516  				files (364M bytes) | 
| Messages: | 370,102 | 
| Posted today: | 4 |