I posted on the end of a 5-month old thread several days ago, and I suspect this may be the cause for the lack of reply.
My problem also seems to differ slightly from the rest of that thread, so we'll bump, and give the new information here.
I've had this problem on my newly installed WP's. Install, and WP sends standard 'admin' login email. Good.
New user signs up, sends admin notification email. Good.
Sends user password email - not received.
New user attempts password recovery. "Email sent successfully" - not received.
I've traced through the entire registration process as far as email sending, as well as the password recovery process, and I can't make any sense of why it works for half the processes, and not the other. This is problem is always the same - always sends the admin notifications of new users, but never sends anything else (even for admin password recovery).
WordPress is telling me it's version 2.0.5. If I can offer any more assistance in finding the bug, let me know :)
Edit: On a quick review of my 3 WP's, the first is a sub.domain.com/, the other 2 are sub.domain.com/dir. the first is as described above, the 2 in directories appear to send recovery and new user emails and to admin, but nothing else appears to be working.
That was the first post. Nothing much changed, I went through the PHP, put in some echo's, everything appeared 'normal'. I came back and posted a little more info:
Just thought I'd add a little more detail. This is all running on a Debian Linux server using PHP 5.1.6-4, and Apache2. No errors appear to be arising from the mail command, and from what I can tell, it's sending all emails. The problem doesn't appear to be wordpress itself (although it's possible that I missed something in the format of the email itself), rather something between the mail() function in PHP, and the sendmail command? It just seems rather peculiar that half the emails are sending, and half aren't - and it seems to be always the same ones in each group.
Doesn't make a lot of sense near the end - it was rather early in the morning and I was yet to sleep.
It's always the same: The admin 'WordPress created' email always sends. The admin 'New user' email always sends. The user 'Password notification' email never sends. The user 'Password reset' email never sends.
Last night I upgraded to 2.0.6, following the instructions, and nothing has changed. The admin 'New user' email still always sends. The user 'Password notification' email still never sends. The user 'Password reset' email still never sends.
If I have time, I'll go back through the code and see if I can find where it's going wrong, but this task seems pointless if other people are having the same problem and have found their own solutions that they're willing to share.