ISSUE: UNABLE TO VERIFY SERVER
EXACT REASON: this is due to a domain mismatch, between the server address being typed into a mail app & the one inside the SSL certificate being used to encrypt communications.
EXPLAINED: your hosting server uses subdomains to deliver all the business services, like email and shared resources. for instance, the email server is often called by a subdomain , “mail.your-domain.co.uk”, other services use subdomains, like “webmail.your-domain.co.uk” to access your email in a web page. Other subdomains in use for carddav shared address books, caldav shared calendars, webdav cloud-drive and of course the auto-configure services used by your apps.
all the extra subdomains mentioned above are not covered by your existing SSL. in the absence of a valid SSL cetificate to provide cover, the mail server reverts to using a certificate installed on the providers hosting platform, which obviously isn’t in your name. Apple have decided to err on the side of caution and not allow you to make an exception for mismatched SSL in all their apps.
SOLUTION: decide which webhost provided services you are going to use, and buy an SSL certificate to cover them all. basically there are 2 types of certificate for doing this
Cheapest: Multi Domain SSL (upto 3 domains) covers web pages, all email access, calendars* and address books*. typically the 3 domains are (plain)my-domain.co.uk, mail.my-domain.co.uk & webmail.my-domain.co.uk
All Services: Wildcard SSL (unlimited subdomains) covers web pages, email, carddav shared address books, caldav shared calendars & webdav cloud drive.
Use the proper SSL solution & all your iOS and MacOS connection problems will go away along with all the scary “untrusted connection” warnings in normal devices.
*some automatic functions may not work or present warnings