Email Dilemma

Hi! I'm having some issues with emails and my site, and was hoping to get some help on the best way to resolve them.

We would like to send out mass e-mails/newsletters to our existing userbase, and were using Mailgun with bd Mail to fit this purpose. It works well for everything else, but we have a high bounce rate. This is due to a huge mistake we made early on in our forum where we left email validation optional. As a result, we have presumably many incorrect email addresses. I know xenForo handles bouncing by default, but we have an hourly limit of 100 e-mails, and 6,600+ members to send e-mails to and check.

I know of e-mail verifying services, but even if we got a list of the e-mails from xenForo, any incorrect e-mails wouldn't update automatically, would they? Is there any validation service that integrates with xenForo to automatically update the email state (verified/not verified) of the users with incorrect addresses?

Going forward, are there any other recommended changes I should make?

Thanks for your time!