test sendmail with IP addrss only

We will soon be our own ISP. . . I want to test sendmail without changing our registered Domain info because our email is still thru the outside ISP.  Want to test sendmail using only TCP/IP, ex. dave@208.454.xxx.xxx instead of dave@myisp.com.  Can this be done?
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You shouldn't do this because sendmail will behave differently based on the fact that it's user@ip rather than user@domain - you won't be doing a valid test.

What you'll have to do is to set up a DNS server somewhere with the false information on it, and tell the machines you're using to test with to use it as the DNS while you're testing.  

Alternatively, you can change the real DNS information to have the new machine listed as a secondary MX, and then from the test machines firewall out connections to the real machines.
You cannot using ip address when using Sendmail because Sendmail using hostname lookup instead of ip lookup.

You need to have valid hostname and ip address , and also need to setup MX record for your email server on the DNS.

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