• create a new account at Special:CreateAccount, check the box for temporary random password by email, specify an email address
• check email, see temporary password, use it to log in
• it forces you to set a new password
• go to user preferences and the email options are grayed out with a message about validating your email address.

once that new password is set it should also automatically mark the email address as validated.

(did this today at enwiki for MediaWiki version, etc)