Here is the email I just received:
Dear Webmaster,
Your site, https://<mydomain>/, uses an SSL certificate which is not recognized by web browsers. This will cause many web browsers to block users from accessing your site, or to display a security warning message when your site is accessed.
To correct this problem, please get a new SSL certificate from a Certificate Authority (CA) that is trusted by web browsers.
Thanks,
The Google Web Crawling Team
Where <MYDOMAIN> is yjl.im. At first glance, I thought this was new kind of phishing but it's real, the message was also on Webmaster Tools.
First of all, I believe I have never written down http://yjl.im/ anywhere, needless to mention the one with HTTPS. So, I guess Google is very kind to check that for you. If it isn't not this email, I haven't thought about to check it.
And here is a screenshot of the certificate:
The naked domain has URL forwarding to www.yjl.im. I use my registrar's free service, so I have no control of it. If Google App Engine could operate on naked domain, I wouldn't need that.
I don't understand why their servers listen to HTTPS, that makes no sense. Anyway, I might turn off URL forwarding or see what my registrar would say about it or just forget the whole thing...