By mail or through mail

A subtle distinction!

"By mail" typically means that something is sent or received through the postal service, such as a letter or package.

"Through mail" is a less common phrase, but it can also refer to the postal service or a system of communication that uses mail. For example:

• "The company's orders are processed through mail." (Here, "through mail" means that the orders are processed using a system that involves sending and receiving mail.)
• "The application was sent through mail to the hiring manager." (Here, "through mail" means that the application was sent using the postal service.)

In general, if you're talking about sending or receiving something using the postal service, "by mail" is a more common and idiomatic phrase. If you're talking about a system or process that involves mail, "through mail" might be a more accurate choice.