marketpress not sending confirmation emails?

MarketPress question: my install isn not generating conformation emails/shipping emails, etc. even though plugin set-up fields are set up properly. is there a server setting that could cause this? site in question is hosted on vps.net cloud server, with MX records set to google apps account, email from address is primary google apps addy. any special trouble shooting references I could find, quick fixes or known problems with this set-up? didn't find anyone with this problem in forum search. thanks!