If you need to check the Mail Exchanger (MX) record for a domain, you can do so online using an MX Lookup Tool at MXToolBox. Once you have looked up MX information for a domain, you are given the option of running Simple Mail Transfer Protocol (SMTP) diagnostics, which will connect to a mail server via SMTP, perform a simple Open Relay Test and verify the server has a reverse DNS (PTR) record. It will also measure the response times for the mail server, giving you an indication of whether they are good or bad.
You also have the option, after you've looked up the MX information for a domain, to perform a blacklist check. That test will check a mail server IP address against 147 DNS based email blacklists. (Commonly called Realtime blacklist, DNSBL or RBL ). If your mail server has been blacklisted, some email you send may not be delivered. Email blacklists are a common method employed by email server administrators to reduce spam.
