I moved the blog I was working on from my development server (on DreamHost) to the client's server (some local host which they are unwilling to switch from). Everything seems to be working perfectly, except that users are not receiving their new user confirmation emails, or their lost password emails.
I have Contact Form 7 installed, and that sends emails out perfectly, so I know the server is set up to send mail successfully.
I have checked that I have the correct email address in General Settings and in the User Settings.
I have tested a simple mail() script on the server, and that sends just fine:
$message = "Line 1\nLine 2\nLine 3";
$message = wordwrap($message, 70);
mail('firstname.lastname@example.org', 'My Subject', $message);
PHP version is
Where do I even begin with this? My google-fu is not strong today (I get a bunch of crappy posts that don't actually help)... I'd prefer not to have to resort to a plugin to fix this (although I'm happy to use a plugin to temporarily troubleshoot, if necessary).