See https://meta.discourse.org/t/email-address-change-confirmation-email-not-sent-but-every-other-notification-emails-are/165358
In short: with disable emails set to non-staff, email address change confirmation emails (those sent to the new address) are not sent for staff or admin members.
This was happening because we were looking up the staff user with the to_address of the email, but the to address was the new email address because we are sending a confirm email change email, and thus the user could not be found. We didn't need to do this anyway because we are passing the user into the Email::Sender class anyway.
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