How do I get my old xbox gamertag on my new microsoft email account without messing my email up

Hi and thanks for reaching Microsoft Xbox gamer's community. My name is Josef.
I'm an Independent Advisor and a Microsoft Xbox user like you.

Hope you're doing great today despite this 2

If those emails are Microsoft emails (outlook.com, Hotmail.com, etc) you can't do that. Because they're linked automatically to each Microsoft account.

If you want to use the desired gamertag in your main account you need to change the gamertag first. Then change the gamertag on your main account
PS: Sometimes the gamertag is not available right away, you may need to keep an eye on the gamertag change website until the system let's you use it

You can use the email as an alias. But that doesn't mean that the content is going to be transferred between the accounts or similar.

Any content transfer between Microsoft accounts can't be done
In case you need to know more about aliases, check this article :
https://support.microsoft.com/en-us/office/add-...

the account connected to my old gamertag is a microsoft account, but it doesn't have @outlook or @hotmail) and the new email account that I want to be connected to my old gamertag is also a microsoft account but @gmail, not @outlook or @hotmail

I just bought a new xbox and when i set my email up it put my new account on the xbox and im trying to get my old account bk how do i do that

I'm trying to add my new email as alias on my old gamertag but it doesn't work!

I select "Add an existing email address as a Microsoft account alias" and than I put my email @outlook.com when a message comes up "This email address is already taken. Please try another one"

Is there another way to change the email associated to my old gamertag? Thanks