I've been getting absolutely nothing at all - no notification of replies, nor PM, nor email.
In an earlier release of phpBB v3 (maybe RC3 or 4) I had to set up my own board to use an SMTP server instead of the local mail function. Prior to that it seemed to only send out notifications on a whim. One day it worked fine, one day it didn't. I could never track down whether the issue was in phpBB or a problem with my hosts PHP mail service but it seemed to work fine once I switched. Really, notification weren't the main issue - the bigger issue was that activation emails for new users weren't being sent either.
"All forms of monism - whether in political dictatorships, trade monopolies, or monotheistic spiritualities - are detrimental within all of nature, body and soul. They are born of a need for control and power, and they are sustained by force, oppression and fear. Diversity is crucial to health and sustainability." - Emma Restall Orr