Microsoft Outlook is currently experiencing technical issues with users unable to log in or send and receive emails through outlook.com.
Some people have also complained about their outbound emails being rejected as spam.
The issue was reported to Down Detector, with numerous comments between users discussing the problem with their accounts.
In a statement, Microsft Outlook said: "We're investigating a potential issue with Outlook where users may be unable to log in, or send and receive emails.
"We're reviewing systems data to determine the next troubleshooting steps."
The free email service, formally known as Hotmail and Windows Live Hotmail, has created a status page online for its users to stay updated.
Those on social media have taken to Twitter to complain about the issue.
One said: "Madness on twitter today about the #Outlookissues - emails from http://outlook.com email addresses are being rejected as spam! Help!"
Another shared: "My outbound emails are being rejected as Spam to all recipients outside Outlook. Is there a resolution timeline? Anyone else?"
While another replied: "Same here. It seems to be a bigger problem as I see that more have this same issue."
You can follow the live updates on the problem with Outlook here.
