What's going on with this?

I was checking Apple Mail when I received a notice from spamsieve to download version 2.9.16. I closed mail, downloaded and installed the new version, and now Mail doesn’t work. What is going on with this?

I don’t know; I’ve not heard any other reports of problems. Please explain what you mean by “Mail doesn’t work” (e.g. what you did, what happened, and what you expected to happen instead).

Did you try restarting your Mac?