[arsalahmed786]

The solutions is simple:
use different email and difficult password for every different site and store them in an encrypted database.That's all.
Even if one of your email account compromised then the others are still in safe.

Under the user control panel enable these options: 
Messaging and Notification
Receive emails from the Administrators.
Hide your email from other members.

But the question is:
How do they know that you're members at post4vps and yours email addresses? Did you share your address at the forum for the public?
I haven't received such an email, just the genuine one from Dynamo two days ago.

@Abdul Sami
They already know your email address so you can't hide it from them. Generate a new password (don't share your real one) and send it them by pretending that you're requesting a VPS from them. Let's try it out to reveal what do they want.

Yeah right and i think Email addresses leaked from MyBB because it not has much security everyone is write their email address while they apply for a VPS so hacker maybe get email address from VPS request section but how? it possible but not easily.

OR Probably email addresses leak from Profile see attached image.