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I have something in my mind and I want to be reassured:
If the owner of a locked account send an appeal from a new email, will you unlock his account?
edit: the user provides a signed message.
If a signature is provided, probably. But each case needs to be considered separately.
You know that there are many appeal-threads where users already provided their signed message. The hacker will simply create a new email and copy paste the signed message.
I don't know if what I said make sense but it would be better to only accept appeals from the original email the user used to register or to accept only newly signed messages.