“Unknown modifier ‘g’ in…” when using preg_match in PHP?

There is no modifier g for preg_match. Instead, you have to use the preg_match_all function.

So instead of:

preg_match("/^(\w|\.|-)+?@(\w|-)+?\.\w{2,4}($|\.\w{2,4})$/gim", ....)

use:

preg_match_all("/^(\w|\.|-)+?@(\w|-)+?\.\w{2,4}($|\.\w{2,4})$/im", ....)