Please be informed that there is a worldwide issue with the SSL (Secure Sockets Layer) certificate provider, Let’s Encrypt.
This has caused majority email faulty in Windows Outlook.
Our upstream provider is currently in the midst of resolving the issue.for the moment you can using webmail to access email.
Despite advance warning that the expiration date would be on September 30,
when the deadline hit, dozens of users reported issues with a variety of services and websites.
You may refer to this article for more information regarding the incident: