[gentoo-user] The Local Directory path "/var/spool/mail" is invalid.

[thelma]

When I try to select /var/spool/mail I get an error:

The Local Directory path "/var/spool/mail" is invalid. Please pick a
different directory.

drwxrwsr-t  2 root  mail 4096 Dec 10 10:56 mail

Why Thunderbird can not read that directory?