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SOUTHFIELD, MI — November 17, 2005
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This won’t surprise anyone but spammer attacks are on the rise. Computer
Mail Services, Inc. (CMS), an expert in spam and email security, has been
tracking Reverse Non-Delivery Reply (RNDR) attacks and the trend is upward
as the holiday season approaches.
“We’ve seen a 230% rise in RNDR traffic in the last 30 days” says Alan A.
Sitek, VP Development at CMS, “and with Thanksgiving approaching,
this increase perfectly coincides with the holidays, a time when spam volume
is expected to rise further”.
In an RNDR attack, spammers use SMTP mail servers that are compliant to the
specifications requiring the return of a non-delivery report (NDR). This
NDR message goes to the forged sender of the undeliverable message, the
intended spam victim.
An RNDR attack typically avoids filters built into many antispam solutions and
results in thousands of messages to fictitious addresses being sent to your
domain. Spammers know that the contents of the original spam email are
returned to actual email addresses.
Vulnerable mail servers will spend their resources trying to deliver the
NDRs and, if under heavy attack, normal mail delivery will slow. Beyond
this RNDR attacks bring the risk of the domain being blacklisted.
“When fighting RNDR attacks, be aware that some antispam products don’t work
100% correctly”, says Sitek, “and worse, their solutions open the door to
Directory Harvest Attacks, a variant of RNDR. That’s where our Praetor
product is different. It works correctly and completely”.
RNDR, a form of indirect mail relay, was originally announced by CMS in a
June 4, 2003 in a public warning.
ABOUT COMPUTER MAIL SERVICES, INC.
Founded in 1982, Sterling Heights, Michigan-based Computer Mail Services, Inc. (CMS) is a privately
held company with expertise in the development of messaging related products. The company’s
Praetor product protects mail servers of thousands of organizations worldwide.
Praetor is a registered trademark of Computer Mail Services, Inc.
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