Reverse Entries for MX records (mail-in.dynadot.com)
WARNING: Found mail servers with inconsistent reverse DNS entries. You should fix them if you are using those servers to send email.
mail-in.dynadot.com. 166.88.19.15
All mail servers should have a reverse DNS (PTR) entry for each IP address(RFC 1912) Missing reverse DNS entries will make many mail servers to reject your e-mails or mark them as SPAM
All IP's reverse DNS entries should resolve back to IP address (IP → PTR → IP) Many mail servers are configured to reject e-mails from IPs with inconsistent reverse DNS configuration.
In addition:
SOA Minimum TTL WARNING: Minimum TTL value is 2560. Recommended values [3600 .. 86400] (1 hour ... 1 day) Minimum TTL was redefined in RFC 2308 now it defines the period of time used by slaves to cache negative responses
Allow TCP connections WARNING: Couldn't connect using TCP protocol: tcp4:107.22.233.61 tcp4:50.112.111.29 Check your name server's configurations and firewall rules. When response to a DNS query exceeds 512 bytes TCP is negotiated and used all name servers should allow TCP connections (port 53)
Tested on: http://www.dnsinspect.com/dynadot.com/1408786419