Thanks for your response! While you were posting this, I was on the phone with a guy in support who helped me with the key fingerprint strings, and I was able to log on using putty. (The guy was very helpful, considering that he's not trained in shell configurations!)
Not all the instructions on the Shell Access 2018 Transition page were clear - I didn't realize that I should only copy the part of the string after "MD5:" and ":SHA256:", so I kept getting "invalid format" errors. So someone might want to update that page to make it clearer.
I still can't access my email, because I don't know how/where to get it using IMAP. What I need are very specific instructions for setting that up, or a pointer to a tutorial or documentation that has those instructions. I use the shell, but I'm not a sys admin, just a lowly user. :) So if you know what I need to do to get my email using IMAP, could you spell that out, or point me in the right direction?