It appears that Google’s Gmail SMTP (send mail) server might have let their secure certificate expire. I personally just got notified that the smtp.gmail.com server was not secure due to the certificate expiring. Here is a screen capture:
So, it seems like it just expired just minutes ago. I asked others to confirm the issue and they said they are getting the same error.
Scott Hodge did twit about a month ago about the same issue. But this is the first time I am seeing this issue and the certificate clearly shows that it expired just minutes ago.
Postscript: A Google spokesperson told us:
For a short time this morning, some Gmail users sending mail via POP and IMAP saw a notification on their mail clients that the SMTP certificate had expired. We identified the problem and fixed it promptly. We know how important Gmail is for our users, and we apologize for any inconvenience this may have caused.