When you change your email address you receive a verification email:
Confirm your new email address for {Amazing Discourse Website} by clicking on the following link:
http://discourse.example.com/users/authorize-email/{some-long-code-here}
If the user clicks the link a 2nd time (after successfully verifying) the following message is displayed:
There was an error changing your email address. Perhaps the address is already in use?
Consider changing this error message to:
There was an error changing your email address. Perhaps the address is already in use or the email address has already been verified?
Yes, users click links in emails again thinking it’s a new email.
Alternatively if possible just log the user in? If the data is no longer available because the verification code is removed after verification then just updating the message would be great.