A bug bit Gmail on Monday and almost half of the webmail service's users have been affected by the problem, which causes email delivery delays and problems downloading attachments.
Google first acknowledged the problem shortly before 10:30 a.m. U.S. Eastern Time and has been wrestling with it ever since, according to information on the Google Apps Status page.
In an update posted at around 2 p.m., the company disclosed that "less than 50 percent" of users had been impacted, which can safely be assumed to mean that at least 49 percent of users got hit.
Gmail has more than 425 million active users.
In the latest update, posted at 4 p.m., Google said Gmail service had been restored "for most affected users" and that it expects to have the problem solved for everyone affected by 7 p.m. That's three hours longer than the previous resolution estimate.
"We expect a small and declining number of messages to still be affected for the next 3 hours as the remaining delivery backlog is cleared. We are working on several options to accelerate the process and will provide more information when we have an updated time estimate," the note reads.
The Google Docs word processing application and Presentation slide creation application also had a service disruption that started about 10:30 a.m. and lasted until 4 p.m. The company hasn't disclosed the nature of the problem that affected those cloud applications nor the scope of affected users.
The duration of the outage and the number of people affected make this incident a very significant one for Google, which is involved in a brutal fight with Microsoft in the market for enterprise cloud email and collaboration apps.
Monday's outage is affecting not only individuals who use Gmail for free but also businesses, schools and government agencies that use it as part of the fee-based Google Apps suite, as evidenced by multiple Twitter posts and discussion forum threads.
Google Apps competes directly with Microsoft's Office 365, and the two rivals are constantly trumpeting customer wins and sniping at each other's product suites.
A Google spokeswoman declined to comment on the matter beyond what's been posted on the Apps Status site.
Juan Carlos Perez covers enterprise communication/collaboration suites, operating systems, browsers and general technology breaking news for The IDG News Service. Follow Juan on Twitter at @JuanCPerezIDG.