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Using the Block and Accept Filters 59

Chapter 5

Using the Block and Accept Filters

The Block/Accept tab provides a wide range of filters that enhance the default spam and virus

detection capabilities of the Barracuda Spam Firewall. These filters support the use of regular

expressions. For more information on using regular expressions, refer to Appendix 1 Regular

Expressions.

This chapter covers the following filters you can apply from the

Block/Accept tab:

Subscribing to Blacklist Services....................................................... 59

Blacklist Services Descriptions..........................................................60

What Happens if your Domain or IP Address is on a Blacklist........ 61

IP Address Filters.............................................................................. 61

Sender Domain Filters....................................................................... 62

Sender Email Address Filter..............................................................63

Recipient Email Address Filter.......................................................... 63

Subscribing to Blacklist Services

The External Blacklist page (inbound mode only) lets you subscribe to various blacklist services.

External blacklists, sometimes called DNSBLs or RBLs, are lists of Internet addresses from which

potential spam originates. The Barracuda Spam Firewall uses these lists to verify the authenticity of

the messages you receive. If the system receives a message from a sender on a blacklist, the message

is either blocked, quarantined or tagged depending on the blacklist settings.

By default, the Barracuda Spam Firewall uses the Barracuda blacklist service and the spamhaus.org

external blacklist service.

Blacklists can generate false-positives (legitimate messages that are blocked). However, because the

Barracuda Spam Firewall sends notifications when it rejects such messages, the sender will be

notified and legitimate senders will therefore know to re-send their message.

Subscribing to blacklist services does not hinder the performance of the Barracuda Spam Firewall.

Query response time is typically in milliseconds, so delays are negligible. And once the Barracuda

Spam Firewall queries a blacklist service, that query is cached on your own local DNS for a period of

time, making further queries very fast.

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Barracuda Networks 4 Guía de instalación Pagina 59