Answer by Steven Penny for How to send mail from the command line?

You can use cURL. Take a file like this:

From: Sunday <sunday@gmail.com>To: Monday <monday@gmail.com>Subject: TuesdayWednesday

and send it:

curl \--netrc \--mail-rcpt monday@gmail.com \--upload-file a.txt \smtps://smtp.gmail.com

https://myaccount.google.com/lesssecureapps