Difference Between Mail and Courier Shipping

USPS, UPS, DHL, Royal Mail, are these services courier services or postal services. What is the difference and does service level differ?

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Cash on Delivery (COD): What It Is and How It Works

Beginners Guide to Shipping with the USPS

What Does Out for Delivery Mean & How Long It Takes?

Zambia Daily Mail's Courier Service is - Zambia Daily Mail

Carrier vs Courier: Which One Should You Choose? - Eurosender Blog

Courier Services vs. Postal Services: What's the Difference?

Recorded Delivery: The Best Option For Mail

How Long Does Priority Mail Take? - US Global Mail

Difference Between Parcels and Packages