Allow users to change the email address of their account themselves, but (1) require new email to be validated before change is processed (via a verification link sent via email), and (2) keep a database/log of all the email addresses any given user has used to better detect duplicate accounts
Scott Hughes
The main reason we don't allow users to change their email address themselves, and instead require them to have an admin/moderator do it, is because users would otherwise use the tool to get around bans on blocks on duplicate accounts.
For example, currently, if a user is banned from the Review Team, the user could just change their email address on their banned account, and then make a whole new account with their email address. They wouldn't even need two email addresses because they could change the email on the banned account to a made-up invalid one that doesn't even work.