With new install that was sending post messages I'm also now having this same "no post email notification" problem. However, I *do* get new user registration email notifications. Around the same time that I noticed this problem had developed, I also noticed that posts are no longer showing who they were created by (kind of like in THIS forum!) and that's terribly confusing... and the main reason I joined this group! To help possibly point at a common configuration issue I'll describe my system (remember: brand new install all at the same time of WordPress, PHP, and MySQL and nothing yet re-installed). I don't seem to be having any other problems with anything at all (anything, not just WP). Like others, I've the proper configuration and it's not been changed since the time when it did send emails about new posts.
System: XP-Pro (fully updated), WordPress running on my own local IIS 5.1 server with Mercury Email Server. No problems at all showing up in Event Viewer. Access is via domain name on dynamic IP mapped with dynDNS. So if WP caches IP address that could be a problem, but I reiterate that WP does send email messages if a new user registers.
MySQL 4.1.12a-nt, PHP 4.4.1, WP 1.5.2.
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