The library lets you send emails, using MailApp, GmailApp, and Gmail API. The library takes care of parameters, so you do not need to care about which method to use. I had trouble with my project when I wanted to automatically send emails and suddenly for me we’ve reached the daily limit. This is why I’ve decided to make some research and be sure fewer bad things happen in the future.
If you are looking for a deep dive into Google Apps Script powered email sending options you are at the door of enlightenment. In this post from Max Makrov you not only to get an explanation of the options and benefits for sending email with
GmailApp and the Gmail API, but also a handy library,
MmailApp. which makes it easy to switch between all three.