Catching Up With Unfinished Details ... and SMTP

FRAMINGHAM (02/14/2000) - This week, we start off with a couple of amplifications/corrections. First, with reference to last week's column, the RF bug mentioned can be purchased from Gateway Electronics in Denver, (303) 458-5444, for around $15. According to Mr. Miranda (my source for the bug):

"They are in fact Asian ASICs made in Korea and imported by a company here in L.A. that has no telephone number. The range is 100 MHz to around 1000 MHz."

Second, regarding the previous week's missive, a reader, who for some strange reason asked to remain anonymous, wrote to point out that Gearhead stated that SMTP messages are formatted according to RFC 822 (Standard for the Format of ARPA Internet Text Messages), which has largely been superseded by RFC 2045 (Multipurpose Internet Mail Extensions).

He pointed out that MIME "enhances the basic format of Internet e-mail messages [R0822] to be able to use character sets other than US-ASCII for textual headers and text content, and to carry nontextual and multipart content."

Indeed it does.

He also pointed to an excellent request for comment-to-be. It is a useful Internet Security Glossary that you can find at http://search.ietf.org/internet-drafts/draft-shirey-security-glossary-02.txt.

Thanks, Doc.

This week, we'll continue where we left off the week before last with Simple Message Transfer Protocol . . . and where we left off was having said "Hi" to an SMTP server. Although Gearhead explained that TCP packets were used, Gearhead failed to note that the port SMTP uses is 25.

Gearhead also incorrectly cited that the SMTP server replies with a completion code of "200". In fact, the successful response code for the HELO command is "250". A small detail is that the HELO command should be followed by the sender's domain name as in "HELO gibbs.com". Note that most servers don't require the domain to be specified and anyway, you can lie about it if you so please.

So now that the corrections are out of the way, we can proceed. We have the SMTP server now ready to talk to us. First, we need to declare who we are. This is where the MAIL command comes in. We send the command:

MAIL FROM:

And unless the server has some reason for rejecting us - such as our address being in the server's list of blocked addresses - we'll get another "250" back to signal that our command was OK.

Note the use of "< >" required to delineate the sender's name, which, like the domain name in HELO, can usually be fake - servers usually don't check to see if domain names of recipients are valid.

Now we have to say who we want to send the message to:

RCPT TO:

The server may reject the command for a number of reasons, including asking the server to relay messages to domains other than its own (a favorite trick of spammers) or because the user doesn't exist on the server. If you are sending to a number of users, you must use a separate RCPT command for each e-mail address.

Of course the user you're after may not be on the server, so you may want to test to see if the user exists. For this you use the VRFY command:

VRFY fred@fred.com

If the user exists, the server should respond with a "250". Note that all of these responses will usually include some descriptive text. In the case of VRFY, the server should follow the "250" with the e-mail address that will be the actual destination of the message. This allows you to see when e-mail addresses are aliases for other users.

Enough already! Next week, we will finally send a message.

RCPT TO: gh@gibbs.com.

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