Linux Server Security, Second Edition

This is the Title of the Book, eMatter Edition

Copyright © 2007 O’Reilly & Associates, Inc. All rights reserved.

Using SMTP Commands to Troubleshoot and Test SMTP Servers

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reduce one’s UCE load. Depending on the volume of email arriving at your site, how-

ever, they can also increase CPU loads on your SMTP gateway.

SMTP AUTH

SMTP exploits, relaying, and abuse, including UCE, are all SMTP problems; they’re

risks endemic to the SMTP protocol and thus to many SMTP Mail Transfer Agents.

But surely there’s some proactive security feature in SMTP?

Until 1999, there wasn’t: SMTP was designed with no security features at all, not

even the most rudimentary authentication mechanism. But that changed in 1999

with the introduction of RFC 2554, SMTP Service Extension for Authentication

(known more simply as SMTP AUTH), which provided the SMTP protocol with a

modular authentication framework based on the generic Simple Authentication and

Security Layer (SASL) described in RFC 2222.

SMTP AUTH allows your MTA to authenticate prospective clients via one of several

authentication schemes. In this way, you can more effectively control such activities

as SMTP relaying and you can also provide SMTP services to remote users, even if

their IP address is unpredictable.

It’s far from a panacea, and it isn’t even supported by all MTAs, but SMTP AUTH is

a badly needed improvement to the venerable SMTP protocol. Both MTAs ...