On a support page, the company said a "serious issue" with a mail server has left about 1% of MobileMe subscribers without access to e-mails for the last six days. The number represents nearly 200,000 Apple customers.
MobileMe was described as "Exchange for the rest of us," but it has been plagued with technical issues since its launch. Some users reported issues with syncing contacts, backing up data, accessing the Web portal Me.com, and a slow update speed.
In acknowledging its problems, Apple dropped the word "push" from the MobileMe service description. It has also given subscribers a free month of service to make up for the bugs, but some customers are still upset.
"I think it has incredible potential, and the convenience is simply fantastic," read a note from a user named RodneyW on Apple's support forum. "However there are some pretty significant issues that have been exposed by the MobileMe rollout -- especially for hardcore users of the e-mail service."
The service is also facing harsh criticisms from some of the most high-profile reviewers in the tech industry.
Even regular Apple fan Walt Mossberg of The Wall Street Journal was disappointed. "If Apple does get MobileMe working smoothly, it could be a terrific service. But it's way too ragged now," he said.
New York Times tech columnist David Pogue called the latest technical snafu a "MobileMess," and was critical of how Apple was reacting to these problems.
"But the real problem is how Apple is responding," Pogue wrote. "For a company that's so brilliant at marketing, it seems to have absolutely no clue about crisis management."