I used DAVx5 on my Motorola Moto G3 to sync with my calender at web.de without any issues over the last month. Today I wasn’t able to sync and DAVx5 came up with the information, that it found an unknown X509 certificate. Following this message there are several details listed (CN=hsp.gmx.net, O=1&1 Mail & Media GmbH…) and I have to check “I checked the full checksum manually” (translated from German) to accept the certificate.
I unsuccessfully tried finding information about the correct checksum at web.de website. Is there another way to check a certificate for authenticity?