Some background info: I have a website (lets say 'example.com') running off a LAMP server (ubuntu 10.04), and all mail traffic is handled by an external email service. My DNS records are set so that the MX records are pointing to the external email server (that all works fine). Postfix is installed but not configured (I believe I need a 'null client' set up?). PHP ini's sendmail_path is set to default. I have little understanding of sendmail (and mail in general), but I can see it is on the default php sendmail path. So I'm trying to send emails from firstname.lastname@example.org to clients through PHP's mail() function, and obviously no emails are being sent. How can I fix/track whats happening (whilst keeping the MX records untouched)?
If postfix is not configured and started your emails will get queued . You can see them issuing 'mailq' from shell. You should configure your postfix to either send all emails by itself (autonomous system) or vía an smarthost (maybe your domains server). How to do it depends very much on your website hosting (does it allow direct mail sending?) and your mail hosting (will it accept relaying from your website?).