Outlook still has my old email address embedded somewhere how to get rid of it

Remove the old address from your Microsoft account’s security information, because verification codes are sent to a primary alias or an address registered as a sign-in verification method—not from an Outlook mail setting.^1^

Replace the old verification address

1. Sign in to your Microsoft account’s Security basics page.
2. Select Advanced security options → Get started.
3. Choose Add a new way to sign in or verify.
4. Add your new email address, mobile number, or Microsoft Authenticator.
5. Enter the code sent to the new method and confirm that it appears in the security-information list.
6. Expand the old email verification method and select Remove.^2^

Add and verify the replacement before removing the old address. Replacing all security information at once can trigger a 30-day restriction.^3^

If the old address is also an account alias

An alias is an address attached to the same Microsoft account, inbox, password, subscriptions, and settings. Removing it from security information does not necessarily remove it as an alias.

1. Open Microsoft account → Your info → Manage how you sign in to Microsoft.
2. If the new address is not listed, select Add email and verify it.
3. Make the new address the primary alias if necessary.
4. Select Remove beside the old alias.^1^

Before removing an alias, verify that it is truly expendable. If the old address is a Microsoft-domain address such as @outlook.com or @hotmail.com, deleting it can permanently delete that address; it may not be reusable.^4^

If the old verification address is already inaccessible

• Another verification method still works: use that method to sign in, add and verify the replacement, and then remove the old address.
• None of the listed methods works: at the Verify your identity screen, select I don’t have any of these and replace the security information. Microsoft then requires a 30-day waiting period before normal sign-in access is restored.^3^

Until these account-level entries are updated, changing the displayed sender address inside Outlook alone will not change where Microsoft sends verification codes.

References

1. Change the email address for your Microsoft account | Microsoft Support
2. How to access Outlook.com when traveling | Microsoft Support
3. Troubleshoot Microsoft verification code issues | Microsoft Support
4. How to delete/update my backup/old email address? - Microsoft Q&A