Dear MIRJANACELEST,
Thanks for using Microsoft products and posting in the Community.
I understand that you would like to add another email address to your account. You can achieve this by adding aliases.
You can refer to the following information:
You can directly go to https://account.live.com/names/manage Then Click Add email, then create and add a new alias Under Add an alias. Tip: Please do not delete other aliases.
This will give you an additional email address that uses the same inbox, contact list, and account settings as your primary email address. You can choose which email address to send mail from, and you can sign in to your Outlook.com account with any of your aliases—they all use the same password.
For more detailed information and steps, you can refer to this link: Add or remove an email alias in Outlook.com - Microsoft Support
Hope this help you, please feel free to let me know how it goes. If there is any deviation in my understanding, please forgive me and provide me with more details. I am more than happy to continue to help you.
Best Regards,
Addie.C - MSFT | Microsoft Community Support Specialist