We sincerely apologise for the inconvenience.
A mail client running on an Apple device will require you make an exception if the SSL certificate provided by the server doesn't match the hostname you’re connecting through. If this SSL certificate is changed or renewed, which will happen at least once a year, another exception needs to be made.
By default, the mail server we advise you to use utilises your own domain name (e.g. mail.yourdomain.com). This allows you to connect through a mail client, but if you attempt to connect with SSL enabled this will show a warning like: Certificate Mismatch. The recommended method of enabling secure connections is to connect using the mail server's actual hostname (e.g. mail123.extendcp.co.uk) - this is a free service we provide that saves our customers the expense of purchasing their own Mail Server Security Certificate.
Most mail clients will allow you to either ignore the warning or provide an exception. Apple devices should let you do this the first time you connect, but when our SSL (*.extendcp.co.uk) renews, Apple devices will show another Certificate Mismatch error similar to when you set the mail account up, but won't allow you to ignore the warning.
To avoid this problem please change your incoming (IMAP/POP3) and outgoing (SMTP) servers to use the actual hostname of the server. In the sort term, whilst we automate the process, this is available from us though our Contact Us page.
Alternatively, you can just turn off ‘Use SSL’ in the settings by going to:
2. Passwords & Accounts
3. [Your Account]
6. Primary Server
7. Turn Off ‘Use SSL’
10. Advanced Settings
11. Turn Off ‘Use SSL’
This does however mean that your connection to the server will not be secured.
Or you can try to add another certificate exception manually via Keychain. This, unfortunately, isn't something our team is able to provide support on.