By courier or by mail

A classic phrase!

"By courier" typically refers to the delivery of a package or document through a specialized courier service, such as UPS, FedEx, or DHL. This method is often used for time-sensitive or high-priority deliveries, as it provides a faster and more reliable means of transportation.

"By mail", on the other hand, refers to the delivery of a package or document through a postal service, such as the United States Postal Service (USPS) or Canada Post. This method is often used for less urgent or bulk deliveries, as it is generally less expensive and more convenient.

In summary:

• "By courier" implies a faster and more reliable delivery method, often used for time-sensitive or high-priority items.
• "By mail" implies a slower and more affordable delivery method, often used for less urgent or bulk items.