This article originally appeared in TidBITS on 2000-02-07 at 12:00 p.m.
The permanent URL for this article is: http://tidbits.com/article/5794
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Email Attachments: Who Does What

by Adam C. Engst

The hubbub we caused with last week's "Email Attachment Format Explained" article is only just subsiding - indication, I think, that this topic creates strong feelings. It's frustrating when you think you're doing everything right with sending attachments but still can't get one through. This week I'll try to shed more light on the issue, and I also recommend that you read the threads these topics spawned on TidBITS Talk.

<http://db.tidbits.com/article/05787>
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Loose Threads -- First, let me address some questions generated by last week's article, and then I'll look at how you work with attachment formats in the major Macintosh email clients.

Many people seemed confused about AppleDouble, with several asking "Is it a program?" To reiterate, AppleDouble, like AppleSingle, BinHex, Base64, and uuencode, is a file format - a specific organization of related bits. Every file on your hard disk exists in a specific format, whether it be the format created by AppleWorks, Microsoft Word, or StuffIt Deluxe. Some file formats like AppleDouble are handled within other programs almost exclusively, so you're unlikely to see a program devoted to creating and decoding AppleDouble files.

Many people recommended Adobe's PDF (Portable Document Format) as another format that's useful for sending files between platforms. Creating a PDF file is generally as simple as printing; see the TidBITS Talk message linked below for a list of ways to create PDF documents. To read a PDF document, you need Adobe's free Acrobat Reader. One tip that I hadn't realized previously: if you want to copy a chunk of text from more than a single page of a PDF document from within Acrobat Reader, you must first set the Default Page Layout to Continuous in File -> Preferences -> General Preferences. We have no idea what Adobe was thinking when they came up with this interface - who ever heard of modifying the functionality of a ubiquitous command like Copy based on your default page layout?

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<http://www.adobe.com/products/acrobat/ readermain.html>

Another popular recommendation for cross-platform file support was the Zip compression and archiving format that's common in the Windows world. Although utilities for creating and expanding Zip archives on the Mac have been around for a long time, they haven't been particularly well known. That should become less of a problem now that Aladdin has released the shareware DropZip 5.5 (bundled with StuffIt Deluxe 5.5), which enables you to create Zip archives. One of the problems with Zip in the Macintosh world is that Zip by default only preserves the data fork of Macintosh files. Aladdin's DropZip 5.5 (as well as Tom Brown's $15 shareware ZipIt utility) can optionally encode Macintosh files with resource forks in the protective binary packaging format MacBinary before compressing, which lets Zip archives contain Macintosh files without fear of data loss. Unfortunately, a Zip archive with MacBinary-encoded files inside isn't necessarily usable in Windows unless the user decodes using Aladdin's free Aladdin Expander. For more details about MacBinary, see "Macintosh Internet File Format Primer" in TidBITS-445.

<http://www.aladdinsys.com/dropzip/>
<http://www.aladdinsys.com/expander/>
<http://www.maczipit.com/>
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To simplify the lives of less-experienced recipients, you might include information in the body of the message telling them precisely what you're attaching and the details of any compression and encoding formats you've used. Then, if something goes wrong, they have a chance at figuring out what to do, particularly if you included some boilerplate information about how to decode, expand, and open attached files.

Finally, I want to note that although there are lots of "shoulds" when it comes to which attachment formats work, the only absolute answer is the one you can verify for yourself in a particular instance. If there are weird email gateways in between you and your recipient, if either of you are using LAN-based email programs that have not been updated to support true Internet email, or the phase of the moon is wrong, your attachments may come through corrupted. The only solution is to try alternate attachment formats and see what you can make work.

Test It Yourself -- I spent a bit of time sending messages with attachments to friends who use AOL in an attempt to figure out what AOL does with different attachment formats. After I was done, I realized that with a little work in Eudora, I could set something up for anyone to receive the same tests and see how they worked. With a combination of stationery, filters, and automatic mail checks, I've created a simple auto-reply system using a copy of Eudora Pro running on a Power Mac 7100 here. When Eudora receives a message with a specific subject line, it returns a file using a specific encoding format.

For instance, want to see if you can receive an inline GIF encoded with Base64 via your Lotus Notes account at work? Just send the appropriate test message and Eudora will reply. The system checks for new requests every 10 minutes, so it could be 20 minutes or more before you receive a response, depending on traffic. Please use this service only for serious testing, since it's not intended to support extremely high loads.

The four attachment formats I've used are AppleDouble, Base64, BinHex, and uuencode. My ten test files are an inline GIF image, an inline JPEG image, a Word document, a PDF document, a SimpleText file, a Macintosh application (a self-extracting archive), a Windows application (an .exe self-extracting archive), a stuffed Word document, a stuffed Macintosh application, and a Zip archive of two Word files. That provides 40 possible combinations, including one (the uuencoded Macintosh application) that is guaranteed to fail.

To access these messages, visit the Web page below and click the links for combinations that interest you. The system checks for exact matches in the subject lines to avoid loops and reduce the impact of spammers, so I strongly recommend that you don't try to guess at the appropriate subject lines.

<http://www.tidbits.com/resources/516/ attachments.html>

Unfortunately, there's no way to reverse the testing and figure out how to receive attachments on the Mac from random other email programs. That you'll have to do on your own.

Looking at Specific Email Programs -- All that said, here are details on using different encoding formats with each major Macintosh email program.

<http://www.aol.com/>

<http://www.macemail.com/emailer/>

<http://www.eudora.com/>

<http://www.eware.fr/dev/>

<http://www.barebones.com/products/msmith/ msmith.html>

<http://www.cyrusoft.com/mulberry/>

<http://db.tidbits.com/article/05066>
<http://www.sonosoft.com/musashi/>

<http://www.netscape.com/computing/download/>

<http://www.microsoft.com/mac/oe/>

<http://www.ctmdev.com/>

<http://www.cesoft.com/quickmail/qmp.html>

Sending It Off -- As much as my head is reeling with all the details I've tried to bring together here, there are bound to be situations that defy logical explanation and everything you try. In those cases, remember that it's generally not your fault, if you're using one of the programs above, and the best course may simply be to encourage your recipient to try reading mail using a modern Internet email program using a true ISP rather than AOL or some standards-flouting LAN-based email package.