I've recently got a "Welcome to Bitbucket" email. Has alternative text/plain and text/html parts. text/plain has "Email validation", html doesn't. text/plain says "We're excited that you're getting started with Mercurial...", text/html says "We're excited that you've chosen Bitbucket to host your Git and Mercurial repositories..." There are probably others. And this problem may exist with other email templates where both parts are defined instead of one being produced from the other. Suggests an audit is needed.
Issue #8907 resolved