"Cannot verify server identity" message from mail, iOS 10.2.1
I had this problem on my iPhone and I am using dreamhost. I was using old language on my settings page. Please see the work around on this page
https://help.dreamhost.com/hc/en-us/articles/216385537-How-to-set-up-email-on-an-iPhone
It was changing the settings to:
Incoming
imap.dreamhost.com
pop.dreamhost.com
Outgoing
smtp.dreamhost.com
Hope this helps.
iPhone 6