This, as a result, will send up a red flag for an MTA and will likely lead to an email being discarded. If the records are configured for mailtrap.io, resolving an IP address with a PTR lookup (Reverse DNS lookup) won’t point to a real domain. PTR Records are a defense used by email servers against spammers, especially those using fraudulent domain names (let’s say, mailtrop.io). If they don’t, or a DNS PTR record simply doesn’t exist, an email is likely to be sent to spam or even discarded.
Before it’s delivered to an inbox, most email providers enforce one simple test they run a DNS lookup simultaneously with a Reverse DNS lookup and compare whether the results match. An email travels across the servers ( MTAs) on the way to the recipient’s email client.