Because so many factors control the transmission of e-mail attachments, no single, simple formula will guarantee success. The best I can do is to offer some basic commandments to follow when e-mailing attachments.

1. Avoid attachments whenever possible by looking for alternatives.
If you are sending a document prepared in a word processor, open the file, select the text and copy it into the body of your e-mail message.

If you are trying to send a document to someone in your own company, post the document on your firm's intranet, if there is one. If you have a personal Web site, post the document there, if it does not contain sensitive information.

2. Coordinate the programs you and your correspondent are using for creating and opening e-mail attachments.
Don't send a documented formatted in Word to a WordPerfect user, for example.
But if you can't avoid dueling word processors, save the document in ASCII, or DOS-compatible, format. Or, when you save the file, use your Save As option and save the file in your correspondent's format.

In many programs, the Save As option also allows PC users to write files in Macintosh formatting and vice versa.
The advice holds for other types of files. You have Lotus1-2-3, she has Excel? Save the spreadsheet in Excel format _ making sure that it is in the version of Excel she has _ before you wing it over to her.

Even if you have the same word processor you have to be careful. Your version of the program may be the latest one, your friend's from 1996. Using your Save As option, save the file in the earlier version to avoid possible conflicts between the two versions.

3. Pay attention to file names. It might be a good idea to avoid long file names for documents you are transmitting.
If you send a file named ``This is my very favorite guacamole recipe" to someone their computer could choke on the attachment. Better to make a copy of the file for transmission and name the copy guacamle.txt.

4. Make sure your e-mail programs are simpatico with each other, particularly when it comes to the method the programs use for encoding the e-mail message and its contents.

The standard these days is MIME, or MultiPurpose Internet Mail Extensions. But there are still e-mail programs bouncing around that use the uuencode/uudecode standards.

Macintoshes, for their part, use BinHex. Mac users can gloat. According to ZDNet Webopaedia, an online computing dictionary, BinHex ``is particularly valuable for transferring files from one platform to another,

meaning from Macintosh to PC and vice-versa.
Generally speaking, however, Macintosh can deal with MIME and uuencode/uudecode as well.
The universal lesson is this: Before you click on the send button, check what coding system your correspondent is using. If the codes are different, flip a coin to see who will change options for the sake of a successful e-mail handshake. Whoever loses can change back later.

Encoding differences are not controlled just by the e-mail package you use. Your portal _ the service that is providing you with access to the Internet and all its wonders _ may have its own special encoding criteria. Even if you and your correspondent are on the same encoding wavelength, your portals may not.

Be careful, too, if you are sending from a stand-alone computer to a computer that is on a network _ and vice versa. Networks, too, can wreak havoc with an attachment that does not suit them.

5. Ferret out what limits your portal places on e-mail size. Some portals are truly stingy, allowing you only to send or receive messages that are 1 megabyte, and sometimes even less.

If that applies to your service _ or to the service your correspondents use _ be sure to compress your files, especially files containing graphics. Most programs used to create a graphic _ be it a drawing or a photograph _will allow users to control the compression ratio. Recipients do not have to have a copy of the program to view the photo.

6. Get help. Several third-party programs are available to open attachments your system can't handle. One is e-ttachment Opener for DataViz.

www.dataviz.com