Hello AzKG
Hi, I'm Karl, an independent advisor and will try to help you with this.
Am somewhat confused by what you actual question based on the problem description. You posted your question in the Outlook.com forum focused on accessing an account via webmail whereas the screenshot you included is for the Outlook desktop program
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PROBLEM: Someone (I know) sent me a new outlook business address email account. I fired it up...I can't send or receive emails...but that's not my problem. Somehow I activated my "Default Email" setting and this is my only email address I can use to answer others emails (when outside of outlook)...since I can't email out I can't get help
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The key words in this description are the words "when outside of Outlook" - that indicates you are asking about accessing an email account via webmail (your browser) - the Outlook desktop program included in your screenshot has no bearing on anything
#1 - What do you mean by someone sent you a "new Outlook business address email account? Was a new email address/account created for you?
#2 - Re: "Somehow I activated my "Default Email" setting and this is my only email address I can use to answer others emails (when outside of outlook)"
Do you mean that when you try to log into one of your 3 live email accounts via webmail (your browser) that it's defaulting to the Outlook web page for your new business account?
If yes, you need to be sure to log out of the account and log back in using this link
It could be that your browser has saved your credentials and if the case, you'll need to clear your browser's cache. If you use a private browser session and can log in without any issues, then it's definitely a browser based problem.
#3 - In answer to your question as it relates to the screenshot you provided
While I'm not at all sure that the Outlook desktop program has anything to do with this problem, the answer to your question on how to change the <default email account> in Outlook desktop is done by
From within Outlook, click on
a) <File> --> <Account Settings> --> <Email> tab
b) select the email account you want to make the default --> click on <set as default>
*** changing the <default email account> in Outlook desktop would never prevent you from using any other account to send emails.