How to Enable Tarpitting to Reduce Spam

Tarpitting is when a server identifies a client’s abnormal email operations, and slows down or “tarpits” the process, preventing spam. For more information: https://www.techopedia.com/definition/1722/tarpitting

With tarpitting enabled, if a sender attempts to issue commands to the mail server before the banner, the connection is dropped:

[root@localhost ~]# telnet test.corp.interworx.com 25
Trying 10.1.16.999...Connected to test.corp.interworx.com.
Escape character is '^]'
HELO test
554 SMTP protocol violation
Connection closed by foreign host.

Set Up:

To enable tarpitting, follow these steps:

1. At the command line, use the text editor to view /etc/tcprules.d/tcp.smtp. It will look similar to the following:

2. At the end of the line beginning with :allow, add the following: ,GREETDELAY="5",DROP_PRE_GREET="1"

3. Run ~vpopmail/bin/clearopensmtp