1. Technical details for IT Support Staff
The JANET CA has changed since the Nexus certificates were originally issued. The new CA root is ‘AddTrust External CA Root’, the old one was ‘GTE CyberTrust Global Root’. The new root certificate is already widely used and we do not anticipate it causing major problems. However the change may cause some mobile devices to give (temporary) errors about the certificate not being trusted or not being able to connect to the server. For any mobile/hand-held device errors please restart the device.
Some UNIX IMAP email clients are likely to show some certificate errors/trust messages. Some older systems assume that the user will take on the responsibility of updating certificate chains etc. Most modern Linux systems, e.g. Ubuntu, Debian, CentOS, etc., should automatically update.
If this affects you when using a Unix system, the system administrator (possibly you) needs to install the root Comodo CA certificate into the trusted certificate store. Visit https://support.comodo.com/ for more details.