Some long time later (year+) I retried and got in. I attempted to change the security settings, but it wouldn’t let me.
Some long time later again, I’m now locked out again.
This whole thing is ridiculous. I know the password, and have access to the account to which it forwards all emails. It should be obvious that their is no IP address which regularly uses this account, and that they are clearly locking out the account owner for no good reason.