If you have devices on iOS 12 and you have session-based authentication, you are probably getting complaints from users that they can’t get their email.  You may have already encountered Detlev Poettgen’s article on this or the IBM technote on the issue.  That technote is helpful, but it left out a subtle, but rather important detail.  You will also  need an internet site document for smtp too or your inbound Internet mail will stop getting accepted.  Read more at this IBM technote.

At least this gave me something to do as I sit here with Mom in ICU.  She does appear to be getting better too.