What application are you using for mail?
What version of Windows/MAC do you have?
Microsoft made some changes which caused the windows live mail program to no longer connect. Unfortunately there is not a fix for this issue, however there are a number of alternatives and work arounds. But as far as using the windows live program go it is not going to be able to connect. So the short answer is the Windows Live Mail application does not support the modern synchronization technologies which they are now using.
I suggest you read through this article which explains everything that is going on and what you can do to use your email: https://support.office.com/en-us/article/Windows-Live-Mail-2012-will-not-connect-to-Outlook-com-45453b92-373b-4bbb-88ca-f8ec74f8e8fd
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