Microsoft is still working to resolve an issue which took its Outlook email service offline for seven hours today, leaving users unable to access their communications.
Those attempting to log-in to their email accounts were met with a 'service unavailable' error message.
The technology giant's Outlook.com platform began reporting issues on Thursday morning and Microsoft confirmed was investigating the cause.
A message on the company's service status website said the fault had left users unable to access emails, and it was 'collecting additional data from the affected infrastructure to aid in our investigation to determine the cause of impact'.
As of 2pm, the site reported that 'impact has been mitigated for the vast majority of previously affected users,' but that further work was being undertaken.
Outlook users attempting to log-in to their email accounts were met with a 'service unavailable' error message
According to web service monitoring platform DownDetector, users across Europe, as well as parts of Africa and India, reported problems with Outlook
In a further response to users on Twitter, Microsoft apologised and said that its engineering team were 'aware and [were] actively investigating' the problem.
A Microsoft spokesperson added that some users had begun to come back online as the company responded to the incident.
'Our engineers are addressing an issue that affected some Microsoft 365 services. Services are starting to improve as a result of the measures we have implemented,' the company told the PA news agency.
The popular email platform supports Outlook, Hotmail and Windows Live email accounts and is estimated to have more than 400 million users, although the number of those affected by the outage has not been confirmed.
Many users took to social media to express frustration at the incident, which left people unable to access their work emails at a time when large numbers are working from home and rely on emails to communicate with colleagues.
The technology giant's Outlook.com platform began reporting issues on Thursday morning and Microsoft confirmed it was investigating the cause
According to web service monitoring platform DownDetector, users across Europe, as well as parts of Africa and India, reported problems with Outlook.
It said issues with Outlook were first reported at around 7am on Thursday morning and since then more than 3,000 reports from users struggling to access the platform were made to DownDetector.
Most of the reports (65 per cent) were in relation to problems logging in to the email service, while 34 per cent concerned accessing the Outlook.com website.
This latest issues came just days after Microsoft suffered a major outage of its workplace applications on Monday.
The company has not clarified what caused the outage — which took five hours to resolve — but said on its service-status Twitter account that it had identified a 'recent change' that appeared to cause problems.
It then rolled back the change and applied other unspecified 'mitigation efforts'.