EbonJaeger It's adding an IMAP remote server to connect to
Thanks! I was wondering why I'd never heard of that setting, even when I was using Budgie. I've always used Thunderbird, and during setup, when I provide my email address, it queries the domain, finds the IMAP server there, and sets itself up. I remember that years ago, I needed to provide that connection information manually, but it was still Thunderbird that accepted it. Mystery solved.