This is an example of using multiple command line tools to verify information about an email server. This is old information for microsoft.com, but the procedure still applies.
First, get the MX record information. You can either do this using interactive nslookup or single line:
Default Server: server.domain.co.uk
> set type=mx
microsoft.com MX preference = 10, mail exchanger = mailc.microsoft.com
microsoft.com MX preference = 10, mail exchanger = maila.microsoft.com
microsoft.com MX preference = 10, mail exchanger = mailb.microsoft.com
maila.microsoft.com internet address = 220.127.116.11
maila.microsoft.com internet address = 18.104.22.168
mailb.microsoft.com internet address = 22.214.171.124
mailb.microsoft.com internet address = 126.96.36.199
mailc.microsoft.com internet address = 188.8.131.52
mailc.microsoft.com internet address = 184.108.40.206
nslookup -type=MX microsoft.com
or if you want to use a public DNS server
nslookup -type=mx microsoft.com 220.127.116.11
When you have the MX server information, see if you can telnet to port 25 of the remote server. As you can - each server has multiple IP addresses.
For example (using the above information)
telnet maila.microsoft.com 25
You should then get a banner similar to this:
220 mail04.microsoft.com Microsoft ESMTP MAIL Service ready at Thu, 7 Jan 2010 05:57:59 -0800
You can do further email acceptance tests using additional commands. The full telnet test procedure is outlined here: http://exchange.sembee.info/network/telnet-test.asp
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