Offline mode - license

Hello, I have a free license and since today i’m unable to connect to my email account:
it gives me an error reporting:

RetrieveLicenseXml failed

the web license page is reachable (https://licensemanager.emclient.com)

The license seems active, woul really need help.
Thank you.

Please see this knowledgebase article which gives the solution.

I’m on OSX, the instructions refer to the win version, are there other solutions?

Just download the certificate on that page and open it in Finder by double click. It will be added to your keychain.

I have tried but it does no work, I’m not even able to deactivate the license I have. As if it does not connect at all to the license server.
Firewall is off and I do not have filters on the network traffic. On a second computer in the same house I have no problems. How shall I fix this?