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Tarpit Configuration

The tarpit configuration page (‘Email->Antispam’, the ‘Greylisting & Tarpit’ tab) allows configuration of the two tarpit flavors that are available on Syneto. By default, when the tarpit service is enabled only the ‘Multiple recipients delay’ tarpit is active. The other type of tarpit, that introduces a user defined delay at the specified level in the SMTP communication, must be manually enabled by the user to be in effect.
To configure the ‘Multiple recipients delay’ type of tarpit, click the corresponding ‘Edit’ button. Two values can be changed: the number of recipients after which the tarpit springs into action and the harshness of the tarpit. The harshness of the tarpit is a function which increases the delay after each recipient seen after the recipient threshold is hit. The harder the harshness the larger increases in delay is introduced with each subsequent recipient.
The ‘SMTP protocol delay’ style of tarpit can be configured in a similar manner, clicking on the corresponding ‘Edit’ button. This time, the configuration options that are available are the delay that will be introduced and the level in the SMTP protocol. It’s possible to select any combination of protocol levels.

Figure 3. Tarpit configuration screen

Useful hints

This is a short compendium of useful hints that may help you get the most out of your greylisting and tarpit systems:

  • the default values provided for the greylisting system are thoughtfully chosen to be able to respond to a large palette of situations; however, if you really need to change them make sure you understand how the
    greylisting process works by reading the introduction to this section
  • use the C-Class greylisting to prevent emails sent by clusters of servers (yahoo, hotmail etc.) to be forever blocked by your greylisting system. This may happen because this type of email providers send the outgoing messages by randomly selecting one server from a pool of several hundreds and the same message, when it will be retried may come with a different IP address which means a different triplet which will get greylisted again which introduces unacceptable delays.
  • use the ‘SMTP Protocol delay’ tarpit flavor in conjunction with the other type of tarpit to further discourage automatic spammers and mails carrying viruses; remember that when you are using this type of tarpit, all the emails will be delayed – there is no way you can separate between a ‘good’ and a ‘bad’ email.