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Note added at 12 мин (2019-11-14 19:11:24 GMT)
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What are the differences between emails and letters?

Email is something you write on computer while letter is something you write by hand.

Email is faster and more efficient, because typing and sending email certainly takes much less time than writing and posting.

Email can be pretty casual sometimes if it's not about business, you can simply type a few sentences without paying too much attention to format. But when writing a letter, one always seems to have a lot to say and the format is kind of strict.


Email is more environmental-friendly, unlike letters, which requires the consumption of paper.
https://www.quora.com/What-are-the-differences-between-email...
Email is money-saving, it's mostly free, but you have to pay for the stamps when trying to post a letter.

http

by post = by snail mail (slang version)

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Note added at 47 мин (2019-11-14 19:46:31 GMT)
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oops, "standard"

"The Perception Of Receiving Snail Mail":
http://www.smbceo.com/2018/10/10/snail-mail-or-email-the-ben...

"Have you ever watched the face of a child who receives snail mail?":
https://patch.com/michigan/westbloomfield/bp--the-joy-and-be...

Причем, возможно, лучше употребить единственное число (как синоним к "почта", "корреспонденция"), если контекст позволяет.

Proposition.