A problem with Microsoft's Hotmail and MSN email service is preventing users from multiple providers from sending messages to the Microsoft email services.

Users of the mail application in Apple's OS X operating system on Monday started reporting that email messages addressed to Hotmail and MSN addresses weren't being delivered. The problem doesn't occur if a copy of the message is sent to the user's own account. Changing the priority setting from 'normal' to either 'high' or 'low' also provides a workaround, users reported on the forum.

Microsoft was made aware of the issues with Apple users on Tuesday. The company acknowledged the problem and said it has been working on a solution. As of Thursday afternoon there was still no fix and Microsoft couldn't provide any background information on what was causing the problems.

Subscribers of the Comcast broadband internet service reported similar issues last week. The provider started blocking all outgoing email sent to Hotmail and MSN accounts after these messages were queuing up on their servers. The issue was resolved on October 20, as vnunet.com reported earlier this week. 

Users of the Canadian broadband providers Rogers and Cogeco have reported similar issues to the ones that face Apple and Comcast clients.

Some user complaints on public fora go back months. Microsoft's refusal to discuss the situation made it impossible to verify those claims and determine if they are related.

Apple PR did not respond to repeated requests for information. A spokeswoman for Rogers said that she wasn't aware of any issues. Cogeco did not return a phone call seeking further information. A spokeswoman for Comcast declined to provide information about the technical background of last week's outage.

Andrew Lockhart, director of product marketing for email security vendor Postini said that the problems appear to be spam-related. An action by Microsoft could have triggered a response from the providers, leading to the outages.

"These things almost become like a comedy of errors," Lockhart told vnunet.com.