A problem with SSL certificates at Google this weekend saw millions of Gmail users unable to send and receive mail for several hours.
The outage followed a lapse in system administration when Google managed to let an intermediate SSL certificate for Simple Mail Transfer Protocol (SMTP) expire.
Google confirmed the problem through its status pages, saying that an "smtp.gmail.com is displaying an invalid certificate".
The firm reacted quickly to the problem, and promised that it was resolved shortly after. "The problem with Gmail should be resolved," it said.
The situation was first noticed by a Twitter user with the @925dk handle and an apparently technological interest, and reports spread quickly.
Gmail has something like 500 million users, and it is not clear how many were affected. Google said only that a "majority" were without full Gmail services.
Google's initial updates were vague on details, saying that users could access their emails and accounts but were facing what was called "unexpected behaviour" when doing so.
"We're aware of a problem with Gmail affecting a majority of users. The affected users are able to access Gmail, but are seeing error messages and/or other unexpected behaviour," the firm reported at 7pm on 4 April.
The last update at 8.46pm, the same day, confirmed an end to the problem, adding: "The problem with Gmail should be resolved. We apologise for the inconvenience and thank you for your patience and continued support.
"Please rest assured that system reliability is a top priority at Google, and we are making continuous improvements to make our systems better."
V3 has asked Google for more information on the outage and is waiting for a response. According to its status pages, the problem has not repeated itself. All other services are, and were, operating as normal.
Last week Google and China clashed over the issue of security certificates after the search giant said it would not recognise security certificates from the China Internet Network Information Centre (CNNIC).
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