To find out your smtp server IP address is clean or blacklisted you need to use Free IP blacklist checker service to check your IP reputation.
What is IP Blacklisting?
ip-blacklist-check

When you send emails based on spam words or spam content to your subscribers or email lists that hit to their spam filter which cause IP blacklisting. There are so many spam filters or spam trappers working right now so you need to be careful while sending emails to your subscribers. Sometime genuine emails to confirmed double optin contact can cause blacklisting due to spam words or links used in Email Campaign.
https://www.massmailservers.net/ip-address-blacklist-check