Four-fifths of spam now emanates from computers contaminated with Trojan horse infections, according to a study by network management firm Sandvine out this week. Trojans and worms with backdoor components such as Migmaf and SoBig have turned infected Windows PCs into drones in vast networks of compromised zombie PCs. At Earth First to reduce the overall load of inbound spam, we use several filtering lists to reject known spam sources.

The Spamhaus list is in use on every server. Spamhaus lists the rather well-known spammers as they move from network to network. Other lists that may be in use on various servers include:

zombie.dnsbl.sorbs.net - this list is used to reject mail from hijacked or "zombied" netspace, where no legitimate mail should originate. This list is in use on every server.
relays.ordb.org - this is the relays portion of the Open Relay Database (ordb), and encompasses verified open relays that are currently used or are likely to be used as injection points for spam. Open relays are typically abused by spammers since they require no authentication for anyone to send mail through them:

smtp.dnsbl.sorbs.net - The open SMTP relay portion of the SORBS (Spam and Open Relay Blocking System) list. Like the above, this is a list of SMTP servers that do not require authentication in order to relay mail through them. Such systems can be and often are used by spammers.
cbl.abuseat.org - the Composite Blocking List from abuseat.org, this list is comprised of open relays, open proxies, and known spam sources.
spews.org - the Spam Prevention and Early Warning System lists, which comprise known spam sources and/or spam support services.

As noted, not all lists need to be in use on every server. Filters are tailored to the needs of individual servers: servers where clients are being spammed dictionary-style (where addresses at the client's domain are selected at random from huge lists - albert, andy, becky, bob....), resulting in hundred of thousands of messages per day, may use all available filters, for instance. Other servers, where spam loads are lower, may use only the default spamhaus list (this is the case on almost all servers at this time).

For the website user we also offer Spam Assassin. This software allows clients to assign scoring to their inbound mail to determine if a piece of mail is spam or not. Options are available to send mail tagged as spam to a special mailbox for later review, or send mail tagged as spam directly to the trash without being viewed. Please note: if you elect to have SpamAssassin send mail tagged as spam to a spam mailbox, please ensure you check and clear that mailbox on a periodic basis. Failure to do so can result in disk quotas being exceeded, which will delay new mail until adequate space is cleared on the account for delivery.

If your mail (or mail sent to you on our servers) is being rejected by our systems due to filtering by any of the above server-level lists, and you believe this to be an error, please contact the helpdesk. Whitelisting of IPs is available to allow mail to come through from senders who would otherwise be blocked. Please forward the entire bounced message to the helpdesk so this process can be completed.

Are there any domains from which mail will never be accepted?

Currently, we maintain a list of domains known to be solely used in spam (that is, they are not domains used for any other purpose than a return address for very large spamming operations).

Any questions regarding spam filtering, either at the server level or the client level, can be directed to the helpdesk.