Question about email forwarding

Here’s the situation!

When I enter mailx -v It will use my .forward file

If I enter mailx -v @somedomain.com
it does not use it.

I’m not a sendmail guru, but is there some setting I’m missing in sendmail.cf?

As well, we just changed company names and domains from setech.com to upspringsoftware.com

If I type mailx -v cammuso@upspringsoftware.com it fails with
User Unknown (Our new domain)

If I type mailx -v cammuso@setech.com it works (Old Domain)

Whatdid I forget to modify?

Thanks

Paul