This is similar to Marcel’s post regarding Windows 7 not supporting TLS 1.1 and 1.2.
It looks like older Apple devices running a version of iOS prior to 11.0 will not have 1.1 and 1.2 enabled so as of right now those devices will not be able to set up one of our hosted mail accounts.
So far I haven’t found any type of work around unless Apple comes out with an update for older hardware to have those enabled.
https://support.apple.com/en-ca/HT208112