Before sending your campaign it's a good idea to test if it will get through spam filters.
When composing your email there is a "Test template" button near the top of the screen (if you don't see this button you just need to save first, hit the "Save template changes only" button at the bottom to save your changes and continue editing). The "Test template" button allows your send a test of your email to any email address, you can also use this to test for spam, here's how to do it:
Go to https://www.mail-tester.com and copy the special email address it displays.
Back in BoltMail hit the "Test template" button and send the email to the test email address. Make sure you set the from address to the same address you will be sending the email from as this can affect the spam score.
Now back on www.mail-tester.com hit the "Check your score" button to see the results.
Understanding the results:
Test emails will always fail some minor checks, for example test messages do not contain a List-Unsubscribe header (because they were only a test and not set to an actual list that can be unsubscribed from).
If you have not set up a verified sending domain for the from address that you used, or you have set it up incorrectly, this will increase the spam score, your email might fail SPF and DKIM checks.