In multiple tests, if your campaign emails all went to the spam folder, it most likely is a problem with your domain name reputation. Domain name reputation is something that you need to essentially highly maintain. It's like your reputation in real life - if you have a bad reputation, most of the people around you, if not all, wouldn't believe anything you say. So if you have a bad domain reputation score, your emails would most likely go to spam as email hosting sites recognize domain name reputation. 

Some things that would reduce that reputation are:

  •  High email unsubscribe rates 
  •  Poor email engagement (for instance, poor email open rates due to poor email quality)

If your domain is new and you just recently started sending emails, it's essential to warm up your domain.

There are a few methods in warming up a domain that you can use, below are my own suggestions:

- Create some sort of email campaign or create multiple with emails with good content to be sent to multiple recipients. These recipients can be relatives, friends, etc. If you could ask them to help you, it'd be great. If they happen to land in the spam folder, just ask them to remove the message from spam into your inbox. Then one of the important things to do is to REPLY to the email that came from your email account and this is something that you can ask them to do as well. 

- Subscribe to newsletters (online) using your Prospect Reach sending domain. Receiving emails is as important as sending them. 

You can search for more methods on the web.