Does USPS Priority Mail have to be in a priority box?

Related questions

1. Does USPS deliver priority mail on Sundays?
2. Does USPS deliver after 5pm?
3. How is priority express mail delivered?
4. Is USPS Priority Mail insured?
5. Does Priority Mail need special envelope?
6. Is it cheaper to use priority mail boxes?
7. Is Priority Mail more expensive?
8. Does Priority Mail deliver on Sundays?
9. Is USPS Priority Mail or First Class faster?
10. Can I ship USPS Priority Mail with my own envelope?

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