Basic setup

Fill out the details in credentials.py
Each line in contacts.txt contains a user's name and email address separated by a space.
message.txt contains the email body.

Instructions for using gmail

Use the hostname 'smtp.gmail.com' and port 587.
Log in with the sender gmail account on the web browser.
Go to link https://myaccount.google.com/u/1/lesssecureapps?pageId=none and set Allow less secure apps to ON.