“There’s a temporary problem” when verifying alias

When I try to add an alias for an Microsoft account, I get the error "There's a temporary problem". I've tried to add the alias several times over the course of a few weeks, on different computers and web browsers, and always get the same error, so I don't think the problem is really temporary.

To try to add the alias, I went to Account aliases, clicked "Add alias", and entered the new alias. I received an email with subject "Confirm your email address for your Microsoft account". When I clicked the link, however, I was redirected to the There's a temporary problem page, which reported, "There's a temporary problem with the service. Please try again. If you continue to get this message, try again later."

It appears that an account at the destination alias exists in some corrupted state. If I try to log in to account.live.com with some random email address, I get the error message, "That Microsoft account doesn't exist." However, when I try to log in with my desired destination alias, I get the error, "You've tried to sign in too many times with an incorrect email address or password."

Yet if there really is an account, I should be reset its password, so I went to the Reset your password page. When I entered the destination alias, I got the error, "The Microsoft account is incorrect. Please try again." Perhaps there is some vestigial alias for some unused account that needs to be manually removed.