The problems began early on April 4th when users tried to send email from Gmail and other messaging services. Google admitted that the problem affected “a majority of users” and caused its services to act in “unexpected” ways.
The company wrote on its App Status Dashboard that the issue was caused by its “smtp.gmail.com” security certificate appearing as invalid to web browsers and apps, meaning that outgoing mail could not be sent. SMTP is the protocol used across the internet to send email.
Security certificates are used online to establish secure, private connections between clients and servers. They enable web browsers to verify that a website is what it says it is and are a vital component of authentication on the internet.
The issue was caused by Google apparently forgetting to renew the security certificate for Gmail. When it expired, apps could no longer verify the credentials presented by the Gmail servers so connections were declined.
The error primarily affected people using Gmail in email client programs and apps such as Microsoft Outlook, OS X Mail or Windows Live Mail, alongside Google’s own Gmail app. Gmail remained accessible through its online interface.
Google hasn’t said how it managed to neglect the renewal of the security certificate for one of its largest services. Its certificates are managed by its own in-house security company, Authority G2.
The issue was fixed around two hours after it was first noticed, but not before the “majority” of users had been affected over the busy Easter weekend when many use services like email to communicate with relations ahead of family arrangements.
