Simplicity and
inexpensive nature of e-mail has made it one of
the most preferred mode of communication even
in business circles. Being the cheapest mode of
communication - most people today prefer e-mail
over telephone or fax. Perhaps the nearest rival
to e-mail today is SMS - which has limited scope
in business communication.
The rising popularity of e-mails has attracted
a whole range of scamsters, professional hackers,
virus writers and mail order businesses to send
mass e-mails. According to one estimate, nearly
half the mails circulating through Internet today
are spam !
Mail Blocking By Spam Filters
Latest survey result by filtering firm MessageLabs
reveals that unsolicited email messages or spam
account for an astonishing 67.6% of the 841 million
emails scanned during April' 2004 (source: businesseurope.com).
If half to two-third of all messages sent globally
are unsolicited - imagine the financial strain
on individuals and corporates who have to sift
through this junk everyday. European firms are
estimated to have lost US Dollar 2.5 billion dealing
with junk mail.
As a result - almost all ISPs use some kind of
spam filter to counter this menace. SpamAssassin
is one such anti spam software - that many ISPs
around the world use.
Unfortunately, spam filters block legitimate
e-mails also alongwith spam. No anti-spam software
can claim to block 100% spam or allow 100% legitimate
mail to pass through. As a result, your legitimate
e-mail may get blocked by a spam filter without
you or your recipient ever knowing about it.
Deliberate Mail Deletion By Recipient
What makes an e-mail suspect in the eye of a
spam filter ? You should know that and make sure
your legitimate e-mails do not look like a spam.
If it does - it will never reach recipient's mailbox.
Worse - neither you nor the recipient will ever
know about it as most spam filters do not inform
the recipient about blocked mail.
Even the recipient may delete the mail without
reading, if it looks like spam. Because of spam
and e-mail-borne viruses - most people these days
check e-mails at server and download these only
after deleting suspect looking e-mails. The decision
to delete an e-mail is mostly based on quick look
at its header - mainly subject. So, if subject
of your e-mail is a suspect - chances are it will
end-up in trash folder 'un-read'
How Spam Filters Work ?
It is important at this point to learn how a
spam filter works so that we can take precautionary
measures to ensure our e-mails do not get blocked
by it. We shall take SpamAssassin as an example
SpamAssassin works by "scoring" each
e-mail message against a range of tests designed
to identify if that message is spam or not. A
wide number of tests are provided, including checks
to see if the sender and recipient address are
valid, if the message dates are valid, if the
body contains any of a list of forbidden words,
if any of the sending servers are blacklisted,
and so on. Each test adds to a message's overall
spam score; messages over a certain user-defined
threshold are treated as spam and can be either
trashed or marked with a special spam header.
In addition to these tests, SpamAssassin comes
with a Bayes algorithm which "learns"
to recognize new spam on the basis of old spam
messages. This makes it possible for the software
to automatically adapt and identify spam even
in the absence of specific header or body tests.
In next issue, we shall discuss specific elements
that make a legitimate e-mail spam suspect as
also how to avoid it.
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