>First, thank you. Do I understand then, that this message about Internet Certificate is benign and I should not worry about it?

Any warning will require attention. There might be something to be done about it.

> I wonder why when I was using Outlook 2010 (on my old computer) I never had this message about Internet Certificate. I will check my old computer (where Outlook 2010 is installed) to see how email account is configured.

Yes, that would be a good idea.