Go to "Email" (left side) -> Mailservermanager -> Hostname= your serverhostname like srv1.domain.tld and domain= domain.tld
in email settings like imap, u must use your servername like "srv1.domain.tld" or mail.domain.tld depends on rdns settings on ur hosting provider and click "rebuild mailserver"
if ur hostname is srv1.domain.tld you must set ur rdns to the same.
if ur hostname is set to mail.domain.tld you must set ur rdns to the same
dont use on mailsettings on your ipad/iphone just the domainname.
u must set it to example:
Server/Host -> srv1.domain.tld or mail.domain.tld or whatever ur hostname is DONT use just the domain.tld (for deeper example:
dont use google.de use myhostname.google.de (srv1/mail.google.de) but replace google with your domain.
as username insert the email like
info@domain.tld - must be created in userpanel for example.
the reason for that is:
The mailserver runs on your host machine with the same SSL certificate like your cwp.
if you insert just the domain xyz.com in E-Mail settings, your certificate tells your iphone "hmpf - xyz.com is not a valid domain i have to secure" and error apears.
if u use your full hostname like mail.xyz.com or srv1.xyz.com (again, depend whatever u have set) the certificate / server tells your iphone "alright! im legit to secure that domain".
dont forget to use security mode = ssl /port 993 (for imap)