Since getting your domain or IP blacklisted can cause a lot of frustration and delivery issues it's important to monitor the health of your domain and IPs regularly to make sure you quickly address any blacklisting problems.
First, is your sender domain verified?
Make sure you have proper SPF, DKIM, and DMARC records in your domain's DNS settings. This page has detailed instructions on how to make this happen.
How to check if your domain is blacklisted
Use blacklist look up sites like MXToolBox. Their look up tool is especially helpful as it also checks the IP that correlates to your domain as well as your domain itself. It is possible that either just the domain or the IP is blacklisted so it is good to check both as either will cause delivery issues.
What to do if your domain is listed
First, you need to make sure that whatever caused your domain to become blacklisted is no longer happening. There are a lot of possibilities, but be assured that blacklist providers won't even consider delisting the domain unless you have a good idea of what caused it and that it is now resolved.
Second, you need to reach out to the blacklist provider who has blacklisted your domain and follow their mitigation process. There are many different blacklist/anti-spam providers and each one has their own process you need to follow. It is possible that you will need to get your hosting provider involved in both steps as you may be using shared hosting or acquired an already blacklisted domain/IP.
Lastly, follow best sender practices to avoid getting blacklisted again. Use double opt-in contacts, remove old and un-engaged contacts, and make sure your emails contain all the required info and unsubscribe methods. Check out our other blog posts that provide more details on best practices.