I've had emails from Spotify, Microsoft, Skype, Steam, and some dating site in the last few months that were the result of some f***tard signing up to those services and using a gmail address the same as one of mine but missing a period within it - eg. fred.nurk(a)gmail.com and the emails are for frednurk(a)gmail.com - all because GMail doesn't count an address with a period as different from one without.
So, for those sites:
1) I click the Forgotten Password link and input the email address, (which will end up in my inbox),
2) log into the site with the new password and proceed to change everything about the account, (address, phone number, CC details, sex, EVERYTHING AND ANYTHING),
3) change the email address to a disposable one using, for example, Mailinator
as something I'm not likely to remember past the next 60 minutes, (eg. email@example.com),
4) wait for the confirmation on the mailinator inbox and acknowledge the change of email address if required,
5) log back into the site with my new email address and change the password to something random, wait for confirmation email if necessary.
6) log out.
Unsolicited crap no longer received and one more happy f***tard somewhere on the planet.
This worked for Skype, Steam, Spotify, and the dating site - Microsoft were kind enough to send an email first asking if it was me that joined up to Live and if it wasn't just don't confirm the email to be removed.
I don't see this a morally objectionable since AFAIAC whether by design or stupidity they have caused this to be my problem, I'm just implementing my preferred solution ... and I have absolutely no qualms about doing it.