You have been mentioned duplicate email
I use wpForo with buddypress and the integration between them is enabled.
That is, it will be mentioned twice, once per plugin, so two emails are sent to the same user.
This can be solved simply by disabling the wpForo email, but it is something I would like to inform to contribute with the plugin.
Thank you for letting us know. I've reported about the issue wpForo plugin developers.
I'll update this topic once I get news for you.
Please navigate to Dashboard > Forums > Settings > Emails admin page, disable the "Enable Email Notification" in "User Mentioning Email"section.
In this case, only the Buddypress mentioning email will be sent.