simple Postfix Problem.
 

I can send and receive emails on the lan just fine also I can receive emails from the internet however I'm unable to send emails to other people on different sites like sbcglobal.net. I have narrowed down the problem in my maillog and it looks like when the other server trys to search for my dns it can't find it. My dns is registered with dyndns and for some reason when i send out emails postfix adds the name of my machine to the dyndns and screwing up the return address. How do i set up Postfix so when I send emails that only my registered dyndns shows up behind the "@" and not the name of my machine with the dns?

any response would be helpful thank you.

example of the email problem: dave@example.dyndns.org somehow gets turned into dave@HOST.example.dyndns.org I can't figure out how to fix this.

also here is a print out of my maillog file:
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Oct 26 01:50:52 SYNapse postfix/pickup[392]: A2340D896F: uid=0 from=<root@SYNapse.prevailingsyn.dyndns.org>
Oct 26 01:50:52 SYNapse postfix/cleanup[543]: A2340D896F: message-id=<Pine.LNX.4.58.0310260150300.539@SYNapse.prevailingsyn.dyndns.org>
Oct 26 01:50:52 SYNapse postfix/qmgr[393]: A2340D896F: from=<root@SYNapse.prevailingsyn.dyndns.org>, size=622, nrcpt=1 (queue active)
Oct 26 01:50:53 SYNapse postfix/smtp[545]: A2340D896F: to=<hopeforthefuture@sbcglobal.net>, relay=vmb-ext.prodigy.net[207.115.63.87], delay=1, status=bounced (host vmb-ext.prodigy.net[207.115.63.87] said: 553 5.1.8 <root@SYNapse.prevailingsyn.dyndns.org>... Domain of sender address root@SYNapse.prevailingsyn.dyndns.org does not exist (in reply to MAIL FROM command))
Oct 26 01:50:53 SYNapse postfix/cleanup[543]: ED2C9D8970: message-id=<20031026085053.ED2C9D8970@prevailingsyn.dyndns.org>
Oct 26 01:50:53 SYNapse postfix/qmgr[393]: ED2C9D8970: from=<>, size=2696, nrcpt=1 (queue active)
Oct 26 01:50:54 SYNapse postfix/smtp[547]: ED2C9D8970: to=<root@SYNapse.prevailingsyn.dyndns.org>, relay=none, delay=1, status=bounced (Name service error for name=synapse.prevailingsyn.dyndns.org type=A: Host not found)
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I only want the from address when i send an email to say prevailingsyn.dyndns.org without it adding the name of my server (SYNapse) to it

ok forget the question above i figured out how to get around that.