Dear finlandsberet ,
I am an independent advisor, and I am trying to help other users in Community with my experience in Microsoft products.
First of all please remove personal information from the screenshot.
This is happening as someone is trying to obtain access to account using that alias from screenshot. Now if that alias is not primary you can go to sign-n preferences (in your Microsoft account) and disable login to your account using that alias. After this whenever someone will try to login with the account he will be receiving error and will not be able to login in.
Also, you can find a lot of suggestions how to secure you Microsoft account here https://support.microsoft.com/en-gb/help/12428/... and here https://support.microsoft.com/en-gb/help/12410/... .
It is also advised to add more security info https://support.microsoft.com/en-gb/help/402647... in order to access or retrieve compromised account https://support.microsoft.com/en-gb/help/10494/...
Also please do not share your account (new alias) and password, pay attention to suspicious emails and do not access links there https://support.office.com/en-us/article/deal-w...
Hope this answers your question and will help secure your account.