vBulletin uses the PHPMailer package to send email.  If you have downloaded 
the phar version of vBulletin then you can obtain a human readable version
of the package by selecting the non phar version of the vBulletin download
in the Member's Area.  The version of PHPMailer used in vBulletin has not 
been modified other than to remove files not necesary for the library to 
function as a security precaution.  You may obtain the full library package
from the GitHub repository located at https://github.com/PHPMailer/PHPMailer. 
You may also obtain the full package by contacting vBulletin support.
