Google's free and business email service is back to full health after stalling for a "majority" of its users -- a number that reaches into the hundreds of millions.
Users were unable to send emails Saturday because the Google server tasked with sending messages had an expired security certificate.
Although users were "able" to access Gmail, the search giant warned of "unexpected behavior."
Google's in-house certificate issuer, Authority G2, reissued a valid certificate, restoring service within three hours of the downtime being reported on its status pages.
It comes just a few days after the company began to blacklist China's main digital certificate authority, China Internet Network Information Center, the organization that manages the .cn domain name.
The decision was made by Google after the Chinese organization was forced to intervene after a delegated company issued a certificate that could've allowed an attacker to impersonate a Google site.
Google ultimately blamed the Chinese parent company for delegating "substantial authority to an organization that was not fit to hold it."