Potential fake E-Mail or Spam Mail Relay
The envelope sender may not be the same as the "From:" line in the message itself; it can be used by a mail server to prevent the message from being sent. And, of course, there's nothing to prevent the sender from using an address that doesn't exist, or that the sender doesn't own.
Appears to be a reputable and long lived website with many respectable customers but ACTUALLY is a conduit through which a great deal of junk ends up filling my inbox unbidden. Affiliate programme managers responsible seems to be 'Modern Ad Media'.