It’s fixed. That’s the good news. The bad news is that the tech giant still isn’t certain what caused nearly half of their email service users to experience delays for 10 hours.

A Gmail glitch that took about 10 hours to fix and hit close to 50 percent of the webmail service’s users has been fixed, ending one of the longest, most widespread Gmail disruptions in years.

Affected users endured email delivery delays and difficulties downloading attachments due to a still unexplained bug first acknowledged by Google at around 10:30 a.m. U.S. Eastern Time Monday. The company declared it patched at 10 p.m.