About ten million users of Google's Gmail service faced delay in sending emails on 24 September due to dual network failure, in which two separate breakdowns knocked out some of the mail service's redundancy.
Gmail users experienced outage for about 12 hours from 15:00 BST on Monday, which resulted in their messages not being delivered for a few seconds (2.6 seconds), while others hit with severe delays.
Google said that the firm apologises for the duration of today's event and it is aware that prompt email delivery is an important part of the Gmail experience, and the latest experience fell far short of the company's standards.
"Please rest assured that system reliability is a top priority at Google, and we are making continuous improvements to make our systems better," the search engine major said.
"We have analysed the data on user impact and are providing a preliminary assessment of what occurred."
Google also noted that the latest outage did not affect users' access to the Gmail page or other functionality.
In April, Google's web services including Docs, Drive and Gmail experienced service disruptions for about two hours, while in December 2012 Gmail suffered a global outage that left millions of its users with difficulty in accessing any of its services.