>We were having some deliveribilty issues with Office365 just putting everything in the Junk Mail no matter what we were trying. I found a write up on the issue from someone else who had the same issue and the solution (for them) was basically, pay Mailgun for a dedicated IP. It was going to be a tough pill to swallow because we send, MAYBE, 200 emails a month (they're basically for password resets and such, not mailing list blasts). Their support basically refused to take my money and switched us to a different sending server that day and our emails were no longer hitting the junk folder within possibly less than two hours of first contact with their support.

I literally went through the same problem, and they did the same thing for me, they didn't accept money for a dedicated IP

It seems that spammers are using their free tier to send spam emails, and because of that, some of their non-dedicated IP range are listed as spam by Office365/google