Wonder if someone can help here.

When I open outlook, I am now getting the following warning.  It happens on both my desktop and laptop.  Email accounts I use include a couple of gmails, an xtra account and two email addresses through domainz using our own domain name.  Both are windows 10 machines.

I'm not sure whether I should have done this but I did install the certificate!  But this didn't solve the issue.  Hopefully, no harm done??

Can anyone help / throw some light on this please.