Reminder: After Jan 3rd clients must use SSL/TLS for email!
If you are unable to send or receive email, please check your settings and ensure SSL/TLS is enabled and that the inbound and outbound servers are correct. For mobile devices, this is usually in the account settings, and has an 'enable SSL' option.
If you are using webmail, please ensure you are using https://yourdomain.com/webmail (Replace yourdomain.com with your actual domain!).