User manual BARRACUDA SPAM VIRUS FIREWALL V4.1 ADMINISTRATOR GUIDE

[. . . ] Barracuda Spam & Virus Firewall Administrator's Guide Version 4. x Barracuda Networks Inc. Campbell, CA 95008 http://www. barracuda. com Copyright Notice Copyright 2004-2010, Barracuda Networks www. barracuda. com v4. 1-100528-01-0528 All rights reserved. Use of this product and this manual is subject to license. Information in this document is subject to change without notice. Trademarks Barracuda Spam & Virus Firewall is a trademark of Barracuda Networks. [. . . ] When receiving a message from a domain, the Barracuda Spam & Virus Firewall can check the signature of the message to verify that the message is, indeed, from the sending domain and that the message has not been tampered with. Because most spam messages contain spoofed addresses, DomainKeys can help greatly in the reduction of spam. DomainKeys uses a public and private key-pairs system. An encrypted public key is published to the sending server's DNS records and then each outgoing message is signed by the server using the corresponding encrypted private key. For incoming messages, when the Barracuda Spam & Virus Firewall sees that a message has been signed, it will retrieve the public key from the sending server's DNS records and then compare that key with the message's DomainKeys signature to determine its validity. If the incoming message cannot be verified, the Barracuda Spam & Virus Firewall knows it contains a spoofed address or has been tampered with or changed. The benefits of enabling this feature include: · Email sender is validated · Email body is validated · Validation through DNS is difficult to foil Advanced Configuration 65 · DomainKeys works well with email forwarding because it doesn't deal with the relay server IP address You can choose to tag, block or quarantine both DKIM signed messages that fail the DKIM database check as well as unsigned messages, depending on how you configure DomainKeys Inspection on the BLOCK/ACCEPT > Sender Authentication page. You can also exempt domains from being tagged, quarantined or blocked if they fail this check. As stated elsewhere in this guide, it is safest to NOT exempt domain names from any kind of spam filtering due to the possibility of domain name spoofing by spammers. DomainKeys inspection does require more CPU resources to encrypt & decrypt the key and is turned off by default. Custom policies Organizations can define their own allowed sender domains or email addresses for sender authentication using the BLOCK/ACCEPT > Sender Email and BLOCK/ACCEPT > Sender Domain pages, but the safest way to indicate valid senders on the Barracuda Spam & Virus Firewall is to whitelist (allow) the IP addresses of trusted email servers on the BLOCK/ACCEPT > IP Filters page, then blacklist (block, quarantine or tag) their domain names on the BLOCK/ACCEPT > Sender Domain page to prevent domain name spoofing. Recipient Verification LDAP lookup On the Barracuda Spam & Virus Firewall 300 and higher, email recipients can be validated with your existing LDAP server. Configuration of LDAP lookup is done by domain from the DOMAINS > Domain Manager page. After clicking Manage Domain for the selected domain, you'll configure LDAP on the USERS > LDAP Configuration page. See the online help on that page for details about entering your server details. If LDAP is not configured, the Barracuda Spam & Virus Firewall will do SMTP recipient verification through RCPT TO commands. LDAP server types supported include Active Directory, Novell eDirectory, Domino Directory and OpenLDAP. Explicit Users to Accept For (Valid Recipients) If LDAP lookup is not being used for recipient verification, the Barracuda Spam & Virus Firewall provides a local database with which email recipients can be compared for validation. "Valid Recipients" can be specified either at the global level from the ADVANCED > Explicit Users page or at the per-domain level from the DOMAINS > Domain Manager > USERS > Valid Recipients page. To administer the local database, either at the global or domain level, fill in the text box in the Explicit Users to Accept For section of the page, entering each email address for which the Barracuda Spam & Virus Firewall should accept email. If you select Yes for the Only accept email for these recipients feature, email will REJECTED for any email recipients not in the list. Note that domainspecific lists override the global list. 66 Barracuda Spam & Virus Firewall Administrator's Guide Alias Linking Alias linking allows quarantined email from multiple accounts to be directed to one account when using per-user quarantine. In the ADVANCED > Explicit Users page you can specify the email addresses to be linked together in the Explicit Users to Accept For and Alias Linking text box. See the online help on that page for more details. The quarantine account for all of the linked email addresses will be associated with the first email address. Make sure to also enter the first email address on a separate line as well. 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