I need to add a hash key to users on register, generated from their email address and the current time, I added the field 'field_subscription_key' to user's fields and I hooked into
custom_newsletter_mail_user_insert(&$edit, $account, $category)
in module's .module file, I have no idea how can I get the email address and time the user was created from these above parameters.
Also, I don't know how to get the user entity, so I would insert the hash key.