I haven't ever used it, never signed a petition, but isn't change.org only about petitions?
I can kinda see their reasoning.. They may even have had their hand forced to do it.
Loads of people who want their way probably signed up with tons of accounts to skew the results. If it's going to work, I guess they need to be able to show that they're legit, out at least that change.org are doing their best to make it that they are.
It's easy to set up one gmail account for example and use it a million times with moving a dot throughout the name or putting a plus sign and anything after the username but before the @ symbol.
They still require you to confirm the email by clicking a link sent to that email, although someone mentioned that this may be an option to the creator of the petition
I do understand the requirement of not using . or + but blocking mail@ info@ seems too extreme to me.
Automailers often have names like that i.e. noreplymail@companyname.com so it may be more about stopping spam or stopping people from using spam email accounts.