Google 'finds' missing G-mails on tapeIt said that the e-mails were "never lost" and that "things should be back to normal for everyone soon".
Many of the missing e-mails are backed up on tape, hence the delay in restoring them, the search giant said.
It blamed a software bug for the incident and said just 0.02% of Gmail customers were affected.
Initially it had said that less than 0.08% of its 170 million users had been affected.
"I know what some of you are thinking: how could this happen if we have multiple copies of your data, in multiple data centres?" asked Ben Treynor, Google's site reliability czar, in the firm's official Gmail blog.
"Well, in some rare instances software bugs can affect several copies of the data. That's what happened here," he added.
He said that Google backs up data on offline tapes, which are protected from software bugs.
"But restoring data from them takes longer than transferring your requests to another data centre, which is why it's taken us hours to get the e-mail back instead of milliseconds," he said.
"Thanks for bearing with us as we fix this, and sorry again for the scare," he signed off.