Mailgun is used by the timely warnings system to automate the approval process of the outgoing emails. Each listserv account has the mailgun email as the account editor/owner.
When the Timely Warnings system is ready to send an email, it sends the email directly to the Penn State Listserv system. The Listserv system holds on to the email from the TW system. While it waits, it sends out a confirmation email to an administrator of the particular listserv holding the email. The administrator traditionally would click the approve button, however; in order to automate this process, we use mailgun to intercept that confirmation email, convert it to JSON and send a POST request to our Timely Warnings site with the contents of the email.
From there, the custom Drupal module performs the click on the confirmation link. See the docs on the custom drupal module for more info on that process.
The mailgun system does what it is supposed to do, however, we are currently working on an internal solution so that we do not need to rely on a third party app for one of the more important aspects of the project. More on that when it is finished.
For complete MailGun documentation, please visit https://documentation.mailgun.com/en/latest/