Angry users have flooded Microsoft's support forums with complaints that large numbers of emails have been deleted from Hotmail accounts.
Hundreds of users complained that all of their emails and folders have been completely deleted and replaced with a generic welcome email, usually sent to new users.
Vocal coach Cath Baxter, who created a group on Facebook about the email blackout, told this journalist that support from Microsoft has been "dreadful".
"I received one comment simply saying that I could not get my emails back, that they had gone. I have heard absolutely nothing since"
"I am absolutely appalled at what has happened. So many emails, memories, passwords, I feel like half my life has just been erased. It's like taking all your personal information and just erasing it," she said.
A Microsoft spokeswoman told the BBC that the issue of missing e-mails was not a widespread problem.