postfix php mail problem

I have setup the domain lefleurlingerie.com with a FQDN of lefleur.lefleurlingerie.com which points to a wordpress installation that all works pretty well. My problem is when wordpress tries to send an e-mail out for new users, authenticating users, receipts, contact forms and so forth. I believe this is due to the PHP mail() function not being setup correctly.

I've been through this guide http://library.linode.com/email/postfix … 0.04-lucid">http://library.linode.com/email/postfix/gateway-ubuntu-10.04-lucid but stopped at the Email Virtual Hosting and Sending Email Securely sections because I don't need to host e-mail and i hope to get it working before i worry about security.

I wonder if anyone has any tips for troubleshooting?

I've spent a day and a half reading docs and googling but I mostly end up trying other peoples solutions that don't work for me. I just don't know where to go from here.

If you need more information I'm happy to provide it.