Hi Colleen - I took your IP address and ran it through MXtoolbox's blacklist checker.
https://mxtoolbox.com/SuperTool.aspx?action=blacklist%3a199.15.213.53&run=toolpage
You're actually listed on three blacklists. In my experience, this is a reflection of sending practices that result in high spam complaint rates. My recommendation is to review your email reports across all emails over the past six months and identify which emails drive the highest unsubscribe rates, which can act as a proxy for high spam complaint rates.
I would consider anything above .5% worth review but that's subjective to how much that campaign contributed to your overall send volume.
Additionally, excessive issues with delivering to invalid email addresses can trigger blacklisting. If you have leads/contacts who are highly inactive (no email opens/form fillouts/website visits in past six months) and they were created more than a year ago, they may pose a risk of becoming an invalid email address.
Finally, you can review Spamcop's website for how to avoid landing on their list and for how to be removed.
https://www.spamcop.net/reported.shtml
Rinse and repeat that for the other two blacklists you're on (0Spam, s5h.net).