Security & Privacy
Spam filter service
7 Jun 2002
There is likely a market for a good spam filter service that is easy to use and effective. Most of the ones that we’ve seen require complicated setups, rely on locally installed software, or have limited features.
The ideal service would allow a user to check email through POP3 or IMAP, function as a filtering proxy, and allow users to configure their accounts over the Web.
Email protocols.
Offering both POP and IMAP services is a must. While the majority of email users use POP to check their mail (most don’t even realize they have an option), many users that read mail from multiple locations have turned to IMAP for mail management. Most services only offer POP, making them useless to power users.
Providing an IMAP proxy is more difficult than creating a POP proxy, and since most users don’t use IMAP, it is understandable that existing services don’t offer IMAP. However, IMAP users tend to be power email users and are more likely to purchase advanced email services.
Proxy Server.
The service should provide a proxy server that filters mail as it is checked. Many of the services available work by downloading email from your mail server to theirs. When a user checks mail, their email program checks the filtering service’s server.
We think this approach is inadequate. This approach requires that a user’s mail be stored on the servers of the filtering service, rather than their office or ISP servers. Many offices and ISPs have Web-based or other alternative remote mail access capabilities that would be lost if the mail is no longer on those servers. AOL members, for instance, would no longer be able to access their mail through the AOL interface. Another obvious disadvantage is that corporations may not want potentially sensitive email stored on servers outside their control.
A filtering proxy functions by acting as a middleman between the user and their mail server. The user changes their mail software’s settings to request mail from the proxy server, which passes each mail command through to the primary mail server. As the messages are retrieved, the proxy filters them based on criteria defined by the user. The proxy doesn’t store the messages; it only acts as a filter between the user and their mail server.
Email Filtering.
The user can tell the service how they would like the proxy server to filter the mail and what to do with it once it is filtered. The proxy server will use a rules-based engine similar to that used by SpamAssassin. The user can easily configure the filtering engine by choosing which rules to apply. Depending upon the user’s preference, messages that are recognized as spam are deleted without showing them to the user, forwarded to another address, or rewritten so the subject line contains a tag identifying the message as spam.
A company that provides this service would find a large number of users willing to pay a monthly fee in order to have mailboxes with greatly reduced spam counts.