Gobline\Mailer\SwiftMailer is a subclass of Fabien Potencier's Swift_Mailer class.
It allows to store a default sender in the Swift_Mailer instance.
This avoids specifying (hard-coded) the same sender address with $message->setFrom() for every new message application-wide.
You can install the Mailer component using the dependency management tool Composer. Run the require command to resolve and download the dependencies:
composer require gobline/mailer