There is a website: MX Toolbox [ http://www.mxtoolbox.com ] it’s not just useful toolbox for various website checks but take a look at how logo of the website changes when you performing actual check.
Here is a full list of tools:
blacklist: Check IP or host for reputation
smtp: Test mail server SMTP (port 25)
mx: DNS MX records for domain
a: DNS A record IP address for host name
spf: Check SPF records on a domain
txt: Check TXT records on a domain
ptr: DNS PTR record for host name
cname: DNS canonical host name to IP address
scan: Perform a port scan on the host
whois: Get domain registration information
arin: Get IP address block information
soa: Get Start of Authority record for a domain
tcp: Verify an IP Address allows tcp connections
http: Verify a URL allows http connections
https: Verify a URL allows secure http connections
ping: Perform a standard ICMP ping
trace: Perform a standard ICMP trace route
dns: Check your DNS Servers for possible problems
