CHECK MX RECORDS
This test will list MX records for a domain in priority order. The MX lookup is done directly against the domain's authoritative name server, so changes to MX Records should show up instantly. You can click Diagnostics , which will connect to the mail server, verify reverse DNS records, perform a simple Open Relay check and measure response time performance. You may also check each MX record (IP Address) against 105 DNS based blacklists . (Commonly called RBLs, DNSBLs)
http://mxtoolbox.com/
CHECK BLACKLISTS
The blacklist test will check a mail server IP address against over 100 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 way of reducing spam. If you don't know your mail server's address, start with a MX Lookup. Or, just send an email to ping@tools.mxtoolbox.com
http://mxtoolbox.com/blacklists.aspx
CHECK DIAGNOSTICS
This test 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. If you don't know your mail server's address, start with a MX Lookup.
http://mxtoolbox.com/diagnostic.aspx
CHECK EMAIL HEADERS
This tool will make email headers human readable by parsing them according to RFC 822. Email headers are present on every email you receive via the Internet and can provide valuable diagnostic information like hop delays, anti-spam results and more. If you need help getting copies of your email headers, just read this tutorial.
http://mxtoolbox.com/EmailHeaders.aspx
CHECK DNS LOOKUP
This test will list DNS records for a domain in priority order. The DNS lookup is done directly against the domain's authoritative name server, so changes to DNS Records should show up instantly. By default, the DNS lookup tool will return an IP address if you give it a name (e.g. www.example.com)
http://mxtoolbox.com/DNSLookup.aspx