Hello,
Try checking the
Yahoo full email headers.
Those can be copy & pasted here if you want help looking at them.
There are a variety of reasons why you may not have received the email quickly.
It could have been stuck in your bosses outbox.
The mail server your boss uses for sending email might have been temporarily rate limited with 4xx errors by the Yahoo mail servers.
The Yahoo mail servers themselves might have experienced a problem.
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