# Where will the mail seem to come from?
rewriteDomain=my_internet_domain.uk

# Are users allowed to set their own From: address?
# YES - Allow the user to specify their own From: address
# NO - Use the system generated From: address
FromLineOverride=YES

ssmtp address@example.com <<<$'Subject: testing 1...2...3'

/usr/lib/sendmail -oi -t <<____HERE
Subject: testing
To: recipient@example.net

Here we interpolate the shell variable $result
____HERE

( printf "Subject: random numbernn"
  dd if=/dev/urandom bs=4 count=1 2>/dev/null | od -D -An ) |
sendmail

claws-mail --compose-from-file filename

sudo apt-get update
sudo apt-get install ssmtp

root=rpi3abc@gmail
mailhub=smtp.gmail.com:465
FromLineOverride=YES
AuthUser=rpi3abc@gmail.com
AuthPass=testing123
UseTLS=YES

echo "Testing...1...2...3" | ssmtp myusername@gmail.com

echo "Message body." | mailx -s "Subject line" -a /path/attachment.txt -r "Sender's Name<sender@email.com>" -c recipient2@email.com recipient1@email.com

sendEmail -q -f "me@mail.com" -u "mySubject" -t "someone@mail.org" -s "my.smtp.com" -o tls=yes -xu "mySmtpUser" -xp "mySmtpPw" -m "myMessage"