My Outlook.com online / inbrowser email-account sends emails using my gmail email-address, how to absolutely prevent that?

Details -
Outlook.com apparently can send emails using gmail addresses, if you go through the steps.
However, I had no MS-accounts at all, then, I used my gmail-address to make a Skype-account, it may have involved a verification-code being sent to my gmail-address.
Then I decided to use my open Skype-account to sign-in to Outlook.com for the first time ever ( that outlook-account did not exist before that sign-in ), and suddenly I noticed that Outlook.com uses my gmail-address ( that I used to make the Skype-account ) to send emails, without me having in any way given any types of permissions to do anything like that.

Note - Outlook.com at no point ever asked me to give any permission to do anything like that, so at no point did I ever grant permission to connect or sync the accounts etc. ( Afterwards, I found a setting called sync in the outlook.com settings when trying to delete the whole ms-account, but that was afterwards )


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