What is snail mail and how is it different from e-mail?

Snail mail is a derogatory retronym — named after the snail with its proverbially slow speed — used to refer to letters and missives carried by conventional postal delivery services. The phrase refers to the lag-time between dispatch of a letter and its receipt, versus the virtually instantaneous dispatch and delivery of its electronic equivalent, e-mail. It is also known, more neutrally, as paper mail, postal mail, land mail, or simply mail.

https://en.wikipedia.org/wiki/Snail_mail

It doesn't take as much in the way of motor skills to type an e-mail message as it does to handwrite a "snail mail" letter.

The next difference between "snail mail" and e-mail is the speed in which a message can be delivered.

Another difference between the two kinds of mail is cost. For an e-mail message, the only cost that is incurred is a person's monthly bill for their internet connection. With "snail mail" letters, people have to use a stamp on each letter they write.

Last, but not least, there is a popular perception that a "snail mail" letter, especially a handwritten "snail mail" letter, is more personable than an e-mail message.

https://vocal.media/education/emails-vs-letters-differences-and-similarities
https://www.behaviourworksaustralia.org/emails-versus-letters-what-works-when-and-why