complete rookie sendmail question

[Ken Hawkins]

first.... thank you all for the invaluable amount of info and resorses 
that flow through this mail list.. I hope to one day contribute more 
than I take away.

that said This is what is happening. I have a webserver 'web1.foo.com' 
that is not the mailserver for foo.com (that is mail.foo.com). 
/var/log/maillog has errors like:

Feb 25 07:34:09 web1 sm-mta[98913]: j1PDTdTd098790: 
to=<bar at somedomain.com>, ctladdr=<foo at web1.foo.com> (1002/1002), 
delay=00:04:30, xdelay=00:00:00, mailer=esmtp, pri=120427, 
relay=mail.foo.com. [64.73.41.34], dsn=4.0.0, stat=Deferred: Connection 
refused by mail.foo.com.

as well I am seeing:

Feb 25 00:10:56 web1 sm-mta[88984]: j1P1HLV8081785: 
to=<foo at somedomain.com>, ctladdr=<www at web1.foo.com> (80/80), 
delay=04:53:35, xd
elay=00:00:06, mailer=esmtp, pri=930762, relay=somedomain.com. 
[216.166.63.26], dsn=4.0.0, stat=Deferred: 451 4.1.8 Domain of sender 
addre
ss www at web1.foo.com does not resolve

I beleive this is because the ctladdr should be foo at foo.com and not 
foo at web1.foo.com

how can i configure sendmail for send out mail as foo.com and NOT 
web1.foo.com? is this possible?

am I barking up the wrong tree here to find out why I am not able to 
send mail out...