Filtering

Activator Mail
Virus scanning and spam prevention based on blacklists and user feedback.
http://www.activatormail.com

AppRiver Spam Filtering
An email security company offering hosted spam and virus protection and a scanning engine especially for OEMs.
http://www.appriver.com/

ASSP
Anti-Spam SMTP Proxy implementing platform independent email filtering services.
http://assp.sourceforge.net/

BopSpam
Online POP3 bayesian filtering service.
http://www.bopspam.co.uk

Clapf
An open source email content filter application. Clapf is a modular statistical antispam application with an interface to popular antivirus programs.
http://clapf.acts.hu/

CleanMailOnline
Online Spam and Virus Filtering, filter before mail reaches your computer.
http://www.cleanmailonline.com

CleanMyMailbox
Whitelist-based service that automatically "cleans" mailboxes of unwanted email multiple times per hour.
http://www.cleanmymailbox.com/

CruelMail
Provides spam-proof email accounts. Only allows email from addresses in whitelist. Charges a fee for others to reach the customer's mailbox.
http://www.cruelmail.com/cgi-bin/main.cgi

Dicontas
UK based provider of email filtering, email monitoring and centralized administration services for business users.
http://www.dicontas.co.uk/

Distributed Checksum Clearinghouse
System of clients and servers that collect and count checksums of email messages in order to detect and filter bulk UCE.
http://www.rhyolite.com/anti-spam/dcc/

The Email Laundry
Spam filtering service to block spam and viruses by domain.
http://www.theemaillaundry.com

E-Mail Magician
Automates filter, mailbox, and nickname creation for Eudora Macintosh. Filters on more than 1,000 spam characteristics.
http://www.yav.com/yav/emailmagician.html

Email Solutions
UK firm specializing in hosted spam and virus protection through MX redirection. Subscription based. A 30 day free trial is offered.
http://www.e-mailsolutions.net

Email Systems
Fully managed service which filters viruses, worms and malicious macros and spam. Firm with offices in UK, France and Sweden.
http://www.emailsystems.com/

FakeMX
Providing a service to temporarily reject mail directed at low priority servers.
http://www.fakemx.org/

Filterspam
Spam filter service designed to protect children from junk emails.
http://www.filterspam.co.uk/

Habeas
Focuses on identifying, classifying, tagging and monitoring legitimate email.
http://www.habeas.com/

Katharion
Provides spam and virus filtering services that keep unwanted mail off the network.
http://www.katharion.com

MailArmory
Spam and virus defense for businesses and service providers.
http://www.mailarmory.com

MailControl
Spam filtering protection for your corporate e-mail network.
http://www.blackspider.com/services/mc_spam.htm

MailFilterPro
Web-based spam and virus filtering services for small business.
http://www.mailfilterpro.com

MailPolice
Managed mail service with parental controls, POP/IMAP and Webmail.
http://www.mailpolice.com

Mailprotector
Hosted Spam filtering service. 30 day trial. No hardware, no software required. Also offers POP3, web and Exchange hosting.
http://www.mailprotector.com.au

Mailshell
Offers protection against spam, combined with personalization and privacy for individual email users.
http://mailshell.com/mail/client/fd.html

MailShield
Australian company offers a managed service with protection from viruses, spam, malware, phishing and unwanted content.
http://www.mailshield.com.au

Messagecleaner
Remove viruses and spam mail before they reach your computer.
http://www.messagecleaner.co.uk

MIMEShield
Runs as Domino server task, No template customizations, supports blacklists/whitelists, Spam email categorization, Electronic fingerprinting, Supports multiple Maps/RBL blacklists, Auto whitelist generation on outbound SMTP traffic.
http://www.gessworks.com/WebSite.nsf/page/mimeshield

MX Force
Enables VARs, OEMs, and ISPs to provide world-class managed email security services.
http://www.mxforce.com

MX Lab
A Belgium based company that blocks virus threats and unwanted emails through MX redirection. Also provides archiving and backup services.
http://www.mxlab.be

MX Police
Managed anti-spam, virus and malware protection.
http://www.mxpolice.com

MXLogic
Protects your entire domain from spam and viruses. No software to install or maintain.
http://www.mxlogic.com/

NuXo Technologies
Provides redundant managed email filtering services: protection against spam, virus and failure without changes to the existing installation.
http://www.nuxo.com

Online Spam Solutions
Managed spam blocker and filtering service for small businesses. Blocks spam and viruses through MX redirection. A 30 day free trial is offered.
http://onlinespamsolutions.com

Peer-to-Peer
Anti-Spam gateway which filters out spam and viruses for an entire domain. A 30-day free trial is offered.
http://www.peertopeer.net/

Prolateral Consulting Ltd
UK based anti-spam and anti-virus filtering plus several other internet security services.
http://www.prolateral.com/pages/services/antispam.php

Pyzor
Open source collaborative spam filtering system using digests of messages to identify spams.
http://pyzor.sourceforge.net/

Realmailonly
Email Spam filtering service for businesses. Mailboxes available.
http://www.realmailonly.com

Red Condor
Stops spam before it reaches your network. Managed spam filtering service blocks spam, viruses, spyware, and phishing schemes. A 30 day free trial is offered.
http://www.redcondor.com

Remote Anti Spam
A hosted anti spam filtering service providing simple, anti spam, phishing and virus protection.
http://www.remoteantispam.com

RMX - SMTP anti-forgery protocol
Filtering protocol verifying the sender address through authorization records made available in DNS to prevent address forgery.
http://www.danisch.de/work/security/antispam.html

Securence
Managed spam service offering Anti Spam and Anti Virus filtering technologies.
http://www.securence.com/index.htm

Sender Policy Framework (SPF)
Framework for publishing information through DNS describing a list of ip addresses allowed to send emails from a specific domain.
http://www.openspf.org/

SODA3
Mobile email filtering service for POP3. Filters your view of your mailbox so you only see email from important senders on your mobile device.
http://www.soda3.com

Sophos PureMessage
Email management solution that provides full control over security and usage of corporate email systems.
http://www.sophos.com/products/pm/?_x=3

Spam Arrest, LLC
POP3 service that blocks spam using sender verification methods.
http://spamarrest.com

Spam Cop
Spam reporting service.
http://spamcop.net/

The Spam Eater
Checks your existing POP3 email account every ten minutes and filters spam and viruses. A 30 day free trial is offered.
http://spameater.com/

Spam Filtering for Mail Exchangers
Document offers detailed discussion on how to filter junk mail in incoming SMTP transactions.
http://tldp.org/HOWTO/html_single/Spam-Filtering-for-MX/

Spam Manager Professional
Spam Manager Professional is a windows based gateway filter for SMTP email servers. This filter uses DNSBL Servers to reject junk or spam mail coming from blacklisted servers.
http://www.eontech.com/spammgr

Spam Safe Mail
Network email scanning and filtering service that removes junk emails at the network level before they are delivered to your mailbox.
http://www.spamsafemail.com/

Spam Soap
Managed spam service featuring message store/forward, message archiving, and administration at both end user and domain levels.
http://www.spamsoap.com/

SpamButcher
Fuzzy-logic software based anti-spam filter for Windows systems.
http://www.spambutcher.com

SpamCerbere
Offers spam protection that doesn't require any installation. Based on a challenge-response system. Free service.
http://www.spamcerbere.com/

0Spam.com
Free antispam service for pop, Yahoo, and Hotmail accounts supporting multiple languages.
http://www.0spam.com

SpamDrain
Swedish company filters individual POP3 and IMAP accounts as well as entire domains. No software installations required. Offers a 30-day trial.
http://www.spamdrain.net

SpamFilter for ISP
Proxy software for incomming mail.
http://www.logsat.com/spamfilter/

SpamStopsHere
An email filtering service for businesses or individual domains. 30 day trial offered.
http://www.spamstopshere.com/

SpamTrap
Australian POP3 email spam filtering service requiring no software.
http://www.spamtrap.net.au

Vipul's Razor
Collaborative spam filtering network allowing users to report and filter out matching spam.
http://razor.sourceforge.net/