Here is the TWO Setting for iPhone/iPad with SSL Enable and SSL Disable
SSL Certificate for *.abchk.com requires renewal every year on June.
iPhone user that incoming or outgoing server name use mail.client-domain.com with SSL enable may encounter a warning popup.
Reason for this error : ABCHK SSL Certificate only for *.abchk.com hostname , not client own domain.
To avoid this warning, you can either change your server hostname to mail.abchk.com with SSL enabled, or use your own domain (mail.client-domain.com) with SSL disabled.