Mail server migration - w00t!
Have you ever seen a server with a post-it note on it reading “LEAVE ON, DO NOT TOUCH”? Chances are it was probably the mail server. Email has a lot of components and they all need to play along, so once you have the system working, you want to modify it as little as possible. Security updates only, basically. And certain checks, like making sure that the storage component isn’t getting filled up too much.