Spam Blaster does not support domains that use a catch-all alias.

What is a catch-all alias?

A catch-all alias is a special kind of forwarding address. If a domain has a catch-all alias enabled, the mail server handling mail for that domain accepts mail sent to any address that you haven't specifically created.

Imagine someone sends an e-mail message to testuser123@domain.com. If domain.com has a catch-all alias enabled, the message will be forwarded to the "real" account that has been configured to receive catch-all messages. But if domain.com does not have a catch-all alias enabled, the message will be rejected with an "unknown user" error.

Although a catch-all alias can be a quick and easy way to start accepting mail for multiple addresses without having to configure separate mailboxes, it has a major drawback. Catch-all aliases make combating spam much, much more difficult. Spammers are known to send "dictionary attacks," spam attacks that send the same message to a very large list of dictionary-based email addresses at the same domain (i.e. adam@domain.com, bob@domain.com, etc.). These attacks often contain thousands or tens of thousands of email addresses. Domains with catch-all aliases enabled are not able to deny the message early in the SMTP transaction process based on the validity of the address. They must accept every message and then run that message through the anti-spam engine.

This holds true for people handling their own anti-spam on their server and for Spam Blaster as well. In addition, domains with catch-all aliases enabled consider every email address at that domain valid. This means that our gateways must track statistics for every email address sent to for that domain, causing increased processing time when statistics are compiled, increased load on the gateway, and increased storage needs.