postfix is trying to deliver the message to "vaf.com":
http://www.dnsstuff.com/tools/lookup...af.com&type=MX
I assume vaf.com isn't your domain name. If it isn't,
stop using it. Use "localdomain". You need to make the name of your "domain"/mailserver unique, and not something someone is using on the internet.
make your postfix server have a name like "office". On both computers edit /etc/hosts. e.g.:
192.168.1.199 office.localdomain office
You don't need domain names for an internal setup. Address your mail to howard@office, not howard@office.vaf.com. That way the name resolution will fail rather than trying to deliver your messages to a third party.
Good Luck,
-c