Curl send email by smime text file, from https://stackoverflow.com/questions/14722556/using-curl-to-send-email

mail.txt

From: "User Name" <username@gmail.com>
To: "John Smith" <john@example.com>
Subject: This is a test

Hi John,
I’m sending this mail with curl thru my gmail account.
Bye!

send.sh

curl --url 'smtps://smtp.gmail.com:465' --ssl-reqd \
  --mail-from 'username@gmail.com' --mail-rcpt 'john@example.com' \
  --upload-file mail.txt --user 'username@gmail.com:password' --insecure