A Reverse DNS lookup is a query that will retrieve the domain associated with a given IP address. It's simply the opposite of the well-known DNS lookup which gives IP addresses associated with a domain.
Reverse DNS lookup is commonly used by email servers to track down malicious messages and spam, as it can identify and verify the domain of an incoming email.
Reverse DNS lookup is a key element of the security protocol used by email servers to protect recipients from malicious emails.
Not all sending servers are supporting Reverse DNS lookup, but those that don't are more likely to be blocked by receiving servers. This affects negatively your deliverability.
Yet, all major ESPs (Email Service Providers)'s servers do provide Reverse DNS.
Spam filters are using keyword detection to spot junk emails and make sure your inbox stays clean. This is why you should choose carefully the words used in the subject and body of your emails. Here's is the ultimate list of spam-trigger keyword that you should ban from your email content in 2021!