I invite members to topics every once in a while.
I do it as a more polite way than mentioning them in a post.
That is, it gives them the option of replying or not without it looking to others like they are ignoring the ping because they aren’t interested etc.
If I want to add something to the invite (like why), I message instead.
I don’t know about if they are sent by email but I’m assuming they would be, based on their Profile settings and when they last visited.