Re: My buddypress will not send any mails! User registration not possible, please help :/
I have too little knowledge on this matter.
Well you said it 
Email is a deep and complicated subject however setting up servers to be able to forward mail relatively trivial how that mail is dealt with though once it is actually in transit around the net is where the problems start.
With your lack of admitted knowledge you are best advised to take the issue to your host to resolve really. This isn’t so much a BP or WP issue as a server one and the use of these plugins is a hack to avoid addressing the real issue as far as I can tell, I have encountered all manner of issues setting up LAMP servers and email but have always resolved by correctly installing and configuring mail functions at the server level.
I have a feeling that you simply haven’t configured the plugin with a proper smtp server url to use, I use Gmail for domains on a regular basis configuring the MX records with the main DNS for the domain and have generally no problem using the sendmail programme with WP/BP
You might also be running a mail server and the mx records might not have been set correctly?
Also I must add that of all the many threads reporting issues with email the majority are with bluehost.
Open a ticket with Bluehost as their continued issue are tending to become a PITA and they are supposed to be a WP friendly host.
