Google has blamed a bug within a storage software update for the email wipes affecting thousands of users over the last two days.
Many Gmail account holders found their emails and contacts had been almost completely erased.
Google explained, in some rare cases, software bugs could hit several copies of the data, so it didn't help in this scenario that the company had multiple copies of user data in numerous data centres across the world.
Google also backs up user data to tape, where such software bugs cannot affect data.
However, it also takes longer to restore such data from tape and this is why it has taken Google hours to bring email back to some Gmail users.
Ben Treynor, vice president of engineering and site reliability czar at Google, said the search giant was "very sorry."
"The good news is that email was never lost and we've restored access for many of those affected," Treynor said in a blog post.
"Though it may take longer than we originally expected, we're making good progress and things should be back to normal for everyone soon."
Google also downgraded its estimate of the total number of users affected by the issue from 0.08 per cent to 0.02 per cent of Google Mail users.
At 7:46pm yesterday, access had been restored for a third of the affected users, with Google saying it was continuing to restore the remaining 0.013 per cent of accounts.
Meanwhile, Google has been updating its Gmail Contacts service to make it easier for users to manage their accounts.
Administrators can now quickly add email addresses to groups and pick from a contact's multiple email addresses to use on a group-by-group basis.
The business impact
Nathaniel Borenstein, chief scientist for Mimecast, said the Gmail wipes were a concern for businesses as well as consumers.
Recent Mimecast research showed 85 per cent of under-25s send work related emails or documents to or from personal email accounts, potentially placing their company's data at risk.
"With workers keen to mix and match personal and business technologies in order to maximise their flexibility and productivity, IT departments need to quickly work out how they can protect corporate IP and ensure compliance in the face of this cultural shift," Borenstein said.
"While using personal email accounts for work can give employees greater flexibility, businesses can quickly encounter problems if they allow individuals to send valuable intellectual property outside of the secured corporate environment."
