The notification system is unreliable. It used to work for me, but then stopped for reasons unknown, even by the IT people. Now, after many months, it seems to be working again, if somewhat intermittently.
I tend not to bother answering highly technical, and unsolicited, PMs from members with few, if any, posts. The chances are they arrived via google search, joined, flashed off a post or two and a few PMs, and then disappear for ever. I've wasted enough time answering technical questions that then go unread for months.
Andrew