Updated my SBS 2003 article to include a blurb concerning the Treo 650 and activesync
I finally fixed the issue I was having using a different email account as the primary account on SBS 2003 and ActiveSync with my Treo 650. It involved a bit of tinkering with the default recipient policy and the SMTP virtual server.
http://blogs.slashstar.com/alex/articles/665.aspx