1. Please navigate to Dashboard > Forums > Tools > Debug Tab > Error & Issues sub-tab and let us know what errors you see.
2. On the same admin page navigate to Tables sub-tab and find the _wpforo_subscribes table section. Take a screenshot and attach to your reply.
3. On the same admin page navigate to Server sub-tab and add it in your reply.
Thanks for the reply.
Here are the 3 screenshots of your suggestion. It seems a problem related to the wp_mail function, but why then it worked with the email registration confirmation of the new account?
Second Screenshot (it's not possible to add multiple files attached?)
Number 3
And please ask your hosting support to update MySQL to 5.6 version. The 5.55 is too old.
In any case your problem cannot be fixed from wpForo side, this is not wpForo issue. This is your hosting service issue or wrong SMTP configuration issue. First please deactivate all plugins, test it again. If you still have such problems please follow to these instructions:
1. Ok I see the error and you see too. Please follow to that error instruction and contact to your hosting service and let them know that the PHP mail() function doesn't work.
If you've configured some SMTP plugin please follow to this support topic: https://gvectors.com/forum/how-to-and-troubleshooting/plugin-incompatibility-with-sending-notification-mail-through-smtp-server/#post-12929