[@robin-w Moderator 6 years ago]

1. You should be aware that many spam filters strip messages that do not come from the correct address. So if your site is mysite.com and your email address in wordpress settings>general is fred@gmail.com then it is likely that messages will be dumped in transit. You need to set up email to come from your site eg fred@mysite.com, your hosting provider can help if needed.
2. Just bbpress?
Then you need to see if this is wordpress wide or just bbpress.
Try https://wordpress.org/plugins/check-email/

it could be a theme or plugin issue

Themes

As a test switch to a default theme such as twentyfifteen, and see if this fixes.

Plugins

If that doesn’t work, also deactivate all plugins apart from bbpress and see if this fixes. if it does, re-enable one at a time to see which is causing the error.

If you cannot do this to your site (say because it is live) then use the ‘troubleshooting’ features of this plugin to let you test without affecting other users

Health Check & Troubleshooting

Then come back
and of course

By default, you do NOT receive emails for your own topics/replies, only if somebody else replies on your subscribed topics

so testing would need two email accounts to prove !