Google’s SMTP server, smtp.gmail.com, has just expired a couple minutes ago. Here is the SSL certificate expiration notice:
It appears Google has forgotten to renew the certificate, even thought a Google Groups post had a warning to Google that it would be expiring today:
This is not the first time Google forgot to renew their certificates. They forgot to renew the AdWords conversion tracking certificate in the past as well.
Stuff like this happens. Google seems to be secure but they just forgot to renew the certificate.
Forum discussion at Google Groups.
Update: A Google spokesperson told us:
