I haven't removed that particular email address yet. I have it ready to go but haven't deleted it yet. But here's where I am no doubt confused. I ask how to remove one email address in Outlook365 (the App) but I'm only learning (I think) as of recent, this is called an account, correct?
You say, "If you want to close the account or never ever use the address again, you need to do that in the Microsoft account"... this is where I am at present. I signed into that account with the email address I'm thinking of removing and it's given me the option to check of a list of boxes to make sure I understand what is involved. It's just an email address (or account) I added a few months ago, so it should be safe to remove it without effecting anything else on this system. It is not the email address I am registered to with Microsoft.
But here's where I'm confused again. You said, "If you want to keep the account and have other aliases and just remove this one, do it in account.microsoft.com - or close the account completely."
I'm losing you when you say, "If you want to keep the account and have others and just remove this one"... that's coming across to me as a paradox. Maybe you can confirm what you mean by 'the account'...