Masssay has 1 permission masssay.use. My suggestion is it has 2 seperate ones, 1 for commands(/masssay /spawn)
and 1 for messages (/masssay hello owner). The reason im suggesting this is because its ok for an admin to use the command for a normal message but if he usses a tp command for ex it might cause a lot of problems. So it can be done by people with responsibility like a staffadministrator or a owner or just an admin u trust more.