E-Newsletter: How to send to entire list instantly or at once?

I have installed both the Mailgun Plugin as well as setup the SMTP for them via your e-Newsletter plugin. I have tried using WP_Mail (which I thought would use the Mailgun Plugin) as well as SMTP (recommended). I have tried making the settings "0" which should be unlimited and without delay but it still takes hours to send to a list of 3,000 people and will increase as user base increases. Mailgun can handle sending them all at once without delays so I would like to fix this. Please help, support access has been granted.