Re: Google apps and Contact form(Php send mail) inconsistency.
It isn't only with Gmail -- the servers here will not send mail with a spoofed from header; the from address must be from your domain.
Contact forms shouldn't be going to email in any case; they should be going to a CRM or trouble ticket database where they can be managed properly with status and other metadata.
“Beware of bugs in the above code; I have only proved it correct, not tried it.” --Donald Knuth
"It was as if its architects were given a perfectly good hammer and gleefully replied, 'neat! With this hammer, we can build a tool that can pound in nails.'" -- Alex Papadimoulis (on TheDailyWTF.com)