Having worked with one of the big 3 in Iron Mountain's space, I would advise partnerships with companies already partnered with USPS, DHL, etc. If you want help targeting and reaching strategic partners quickly, let's chat on clarity.

Ask. Try starting at the top then worry about partnering with smaller companies.
Don't stop taking massive action.
Best of Luck,
Michael T. Irvin
michaelirvin.net
My books are available exclusively through Amazon Books. Check out my book "Copywriting Blackbook of Secrets"
Copywriting, Startups, Internet Entrepreneur, Online Marketing, Making Money