The SSL certificate for apm-internet.net was recently revoked with zero notice (it was due for renewal shortly), so we had to quickly replace it. This seems to have caused issues with iPhones and iPads complaining about the certificate, and is affecting users who are using domains that are not supporting their own SSL.
It may be that the devices in question need to add an exception to allow this (as the domain doesn’t match the domain the user is connecting to), as they’ve been running in this configuration for a while without complaining.
If that doesn’t work or isn’t an option, we would suggest using the generic name of mail.overssl.net – this works for POP3, IMAP and SMTP connections.
Please accept our apologies for any inconvenience caused by this.