Fight against Spam: What Administrators can do?

Manvendra Bhangui

Open source platforms like Linux provide many options for administrators to effectively fight against spammers. Upon migrating to Linux, administrators can use secure Mail Transfer Agents (MTAs) like qmail and postfix. At Sify, we have deployed servers using these MTAs to improve security and spam control. An ancillary benefit of deploying Linux-based mail servers is the cost advantage - the total cost of ownership is many times lower than that of deploying a commercial mail server.

Following are some of the effective options for administrators:

1.Controls at your SMTP server

Use a MTA like qmail or postfix which has a mechanism to block network traffic based on various criteria like IP addresses, addresses without DNS entry, invalid envelope, etc. Other essential features include: relay control, support for RFC 2821, RFC 1123, etc., automatic recognition of local IP addresses, blocking of senders using regular expressions, tarpitting (which prohibits the sending (SMTP) server to send e-mail for a specified time to prevent spamming), hop counting (a measure of distance between two nodes in an internet), refusal of connections from known abusers, spam control (reject/tag/accept) using Bayesian techniques, content filtering and in-built virus/spam scanning. Use an in-built scanner (rather than an external virus or spam scanner) to reduce overheads substantially.

2.Using Message Submission Port

This involves running your MTA on a port other than port 25 (the default for SMTP). A standard port for Message Submission is 587. You should enforce authenticated SMTP on this port. Forcing authentication means that spammers will not be able to use your mail server for sending out mails. Another advantage of using port 587 over 25 is, worms that propagate through email, have become ineffective. For more details users are advised to read RFC 2476.

3.Using Bayesian Filter like bogofilter, dspam, spamassasin.

These are extremely good Spam filters. They are able to catch SPAM with above 99% effectiveness.

4.Using Domain Keys

This uses domain-based email authentication, using public-keys advertised in the DNS. "DomainKeys" creates a domain-level authentication framework for email by using public-key technology and the DNS to prove the origin and contents of an email.

Companies that are susceptible to phishing attacks can buy email service from a company like Sify who has implemented DomainKeys. Sify is using DomainKeys submitted to IETF (Internet Engineering Task Force) by Yahoo.

All of their outgoing emails of Sify customers will be signed with DomainKeys. Sify can add a filters to its customers' email systems that drop any unsigned or improperly signed messages claiming to come from its domain thus protecting tens of millions of customers from these phishing attacks.

Can you bank on a single technology?

No single technology can combat spam totally. ISPs, email service providers will have to deploy multiple technologies to raise the cost of spam.

Also all such providers have to be quick to adopt new technology or change strategy with time.It would be unfair to rate the above techniques; each has its own merits. However, together they provide a safety net. Some people may feel that maintaining large number of such applications may be a daunting task. Some may not have the expertise or knowledge to make the best of use of these technologies and hence, would be unwilling to take the time to learn. Still some may be willing to understand the problem and develop a strategy to deal with it.

With self effort and planning, one can effect a dramatic reduction in the spam flow, but it is necessary to continually modify and fine-tune the applications. Sify can offer support to the administrators in the following four ways:

• Implement/Manage a new highly scalable Secure Spam Resistant Mail Server - SifyMail.
• Manage your existing Mail Server and make it SPAM free (protects your current investments).
• Provide a SPAM free hosted solution where you don't invest on any hardware. Here Sify will host the server and deliver SPAM free emails to your own server. You have the added advantage of reducing your bandwidth by as much as 40% (depending on the amount of spam you receive)
• Provide consultancy on setting up your own Linux Mail Server.

Manvendra Bhanguli is Vice President, Software and systems, Sify. He can be contacted esbmarketing@sifycorp.com