Although their new mail was intact, their personal folders, address book entries and saved mail had been deleted.
At least one Hotmail user who inquired about the problem got a not-so-helpful response from Microsoft: "We have done our best to recover any and all lost email in your account. We would like to suggest that you keep a back-up copy of your mails in a Word document."
"It's ridiculous," said George Karimundackal, a computer systems analyst in New York who had been locked out of his Hotmail account since Thursday. "I'm disconnected for five days, and at the end of it, they delete all this stuff."
A Microsoft representative said Hotmail is working "around the clock" on the problem and expects to restore customers' address books and saved mail.
Dozens of Hotmail users have been locked out of their accounts since last week because of a problem that occurred during what the company called "routine maintenance."
The company says the problem with one of Hotmail's servers affects less than one-half of 1 percent of its 67 million users.
Despite repeated inquiries, Microsoft declined to give details on the nature of the problem, the exact number of users affected, when the problem began, or an estimate on when it might be fixed.
Although some people regained access to their accounts last night and today, others say they still are locked out.
Zlati Meyer, a suburban reporter for the Philadelphia Inquirer, said the last time she was able to check her Hotmail account was last Friday. Meyer said she has other email accounts, but she does most of her personal communication through her Hotmail account.
"I'm not completely crippled by it; I'm just socially crippled," Meyer said. "On an inconvenience scale, this is obviously a 10."
Last year, Hotmail suffered several outages and service problems as it expanded its membership.