Leonard is a systems administrator who has been tasked by his supervisor to slow down or lessen the amount of SPAM their company receives on a regular basis. SPAM being sent to company email addresses has become a large problem within the last year for them. Leonard starts by adding SPAM prevention software at the perimeter of the network. He then builds a black list, white list, turns on MX callbacks, and uses heuristics to stop the incoming SPAM. While these techniques help some, they do not prevent much of the SPAM from coming in. Leonard decides to use a technique where his mail server responds very slowly to outside connected mail servers by using multi-line SMTP responses. By responding slowly to SMTP connections, he hopes that SPAMMERS will see this and move on to easier and faster targets.

What technique is Leonard trying to employ here to stop SPAM?

A.
To stop SPAM, Leonard is using the technique called Bayesian Content Filtering

B.
Leonard is trying to use the Transparent SMTP Proxy technique to stop incoming SPAM

C.
This technique that Leonard is trying is referred to as using a Sender Policy Framework to aid in SPAM prevention

D.
He is using the technique called teergrubing to delay SMTP responses and hopefully stop SPAM

Explanation:
Teergrubing FAQ
What does a UBE sender really need? What does he sell?

A certain amount of sent E-Mails per minute. This product is called Unsolicited Bulk E-Mail.

How can anyone hit an UBE sender?

By destroying his working tools.

What?

E-Mail is sent using SMTP. For this purpose a TCP/IP connection to the MX host of the recipient is established. Usually a computer is able to hold about 65500 TCP/IP connections from/to a certain port. But in most cases it’s a lot less due to limited resources.

If it is possible to hold a mail connection open (i.e. several hours), the productivity of the UBE sending equipment is dramatically reduced. SMTP offers continuation lines to hold a connection open without running into timeouts.

A teergrube is a modified MTA (mail transport agent) able to do this to specified senders.

Incorrect answer:
Sender Policy Framework (SPF) deals with allowing an organization to publish "Authorized" SMTP servers for their organization through DNS records.