Remove a email account from the from: dropdown list in a new windows live mail email

How do you remove a email account from the from: dropdown list in a new windows live mail  email? I want to reply to an email from one account, but I to send it from a different account. (It's a long spammy story)

By default, the account I received the email from shows up in the from: line and I have to change it every time and I usually forget. So I just want to delete that account from the list that I can send from. But I don't want to stop receiving email from that account.

Thank you

 Bob

PS

This is in Outlook.com because Windows Live Mail isn't in the list of Categories.