Managing personal Outlook.com account settings, security, and privacy
Hello HeatherM
While MS certainly does send out alerts about suspicious activity, the line
>>
Please use the following validation link to avoid the Microsoft account termination policy. Validate Account
<<
indicates that this is a phishing scam to get your credentials. A legit alert would tell you to review the sign-in activity on your account and proceed from there. It would NOT ask you to "validate" your account.
Without seeing the actual URL that "Validate" points to, will bet that it doesn't point to a legit MS URL. Easy enough to check, hover your mouse over the link and see where it actually points to OR right-click on that link --> select <Copy> and paste it into any text editor (i.e. Notepad). As for the "sender's address" - that's far too easy to "spoof" to make it look legitimate.
How to check your sign in activity
Check the recent sign-in activity for your Microsoft account