Human Interface Detection - an advanced spam protection
Hi,
not sure if this is even possible with ISPConfig, but I've seen a good spam-protection on a system, a HID ("Human Interface Detection"), which works like this:
User A (userA@somewhere.tld) is sending an e-mail to User B (john@example.com) and User A gets an automatic e-mail from the mail server (of example.com) to verifiy, that he is a human. For this, he needs to visit a URL which is provided in the e-mail. Then he needs to enter a captcha and before his e-mail will be delivered to User B.
But he needs to do this only once and it's valid for all e-mail mailboxes on example.com. For doing this, he will be automatically added to the whitelist.
This is just perfect and would be awesome to choose from as spam-protection.