mail() is by default disabled server-wide and it's added to disable function list. You can enable the mail() function through Cpanel.
Cpanel -->Multi PHP INI editor-->Editor Mode -->Choose Home Directory -->add below command:
disable_functions = show_source, system, shell_exec, passthru, exec, popen, proc_open
for disabled all function use the code:
disable_functions = show_source, system, shell_exec, passthru, exec, popen, proc_open, mail, sendmail
