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I use an Apple Mac and regularly email image files in tiff,...

<< Back to: comp.mail.mime meta-FAQ: Help for MIME problems

Question by Tony Lindfield
Submitted on 4/1/2004
Related FAQ: comp.mail.mime meta-FAQ: Help for MIME problems
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I use an Apple Mac and regularly email image files in tiff, jpg or eps format via Outlook Express to a client using AOL on a PC. Although I send the images with Apple Double encoding - suitable for all computers - the images always reach the client saved in MIME format. When the client decodes the images he is unable to either recognise or open the images in Photoshop. No matter which way I try to send the images the problem is always the same. Pdf files however are not a problem. Is the problem at the PC end and can the MIME encoding be switched off? Or does it need to be on and is there a way to convert the files back to a format that photoshop will recognise? I would be very grateful if anyone can offer any help?

Answer by E. Foote
Submitted on 4/14/2004
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Hi Tony,

Apple Double encoding is the same thing as MIME. (Well, technically itÕs a combination of MIME and BinHex. MIME is also called Base64) You are right to send your PC client an Apple Double or MIME encoded file since a BinHex file (meant for Mac to Mac transmission) would be useless to them. Apple Double will split the file into two parts - a data fork and a resource fork. PC's don't have resource forks so they just trash that part.  Possibly your clientÕs email program doesnÕt support MIME, but thatÕs highly doubtful since itÕs the standard.

One big problem is AOL. TheyÕve been known to completely screw up attachments, so to protect your file ALWAYS compress it before sending. Use Zipit. Most PC users have it. When you zip your file, make sure that the MB (means convert to MacBinary) and the LF (means translate linefeeds) settings are turned OFF. They look like little circles. A filled in circle (looks like a black dot)  means itÕs turned on; a hollow circle means it turned off. You just click on the circle to switch the setting.

Another thing to consider is how you save your file. If youÕre in Photoshop and saving the file in EPS format, make sure the encoding is ASCII not Binary. Binary is useless to a PC. If you have any embedded files within your document, they too must be ASCII. Also the preview should be either 1 bit (black and white) or 8 bit (color) tiff, rather than the Macintosh 1 or 8 bit.  If youÕre saving as a TIFF, then make sure the IBM PC byte order is selected. All these options come up when you save the file, so youÕve probably already done that. The way you title your file is important too. Make sure youÕre not using any forbidden characters such as a colon, question mark, extra spaces, more than one period, etc. and that it ends with the proper extension, like .eps for an EPS file. You may already be aware of these weird PC idiosyncrasies. One other thing you may find helpful - if youÕre in say Illustrator, and using fonts that youÕre not sure your client has, convert the text to paths and you wonÕt have to worry about it. Saves you sending them the fonts.  

I learned these things the hard way when sending Mac files to a PC client for the first time. The person could never open anything  I sent. I made many futile attempts, much to her dismay, changing something each time hoping it would work. By the time I finally figured out what the problem was she had become extremely hateful. My mail program, EudoraÕs default setting for encoding is BinHex so IÕd been sending her a BinHex file every time. All I had to do was change it to Apple Double and I had no problem. Peace reigns.

One other note - I found the book Windows for Mac Users by Cynthia L. Baron and Robin Williams invaluable.

Good luck!

E. Foote


Answer by AlTheEldr
Submitted on 5/11/2004
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This discussion gets ugly because information is encoded at four levels each of which has its own function. When everything is going well, all but the innermost level is of no concern to the wetware.

It is perhaps useful to create an email containing text with an image attached and save it in such a way as when you open it in a text editor you see everything as it would be transmitted over the net. (If you don't see a whole bunch of lines at the beginning of the form something colon something that you did NOT enter,then you are not looking at the email as it actually gets transmitted.)

At the out most level the message is divided in the headers and the message body. The headers are the lines with the colons in them. They end with a blank line. The rest of the text is the message body. The headers describe the mail as a whole and provide for routing information.

Here is a sample of the last few lines of a header

Content-Type: multipart/mixed; boundary="part1_1a0.2430f7d9.2dd05110_boundary"
X-JunkMail: NotJunk
X-MFData: [38.473127 v2.1:1 n237 s3712 g73322 b62381 p0.080625 sN11 t0,734451]
X-UIDL: 267541
Status: RO

The lines in the header are highly variable.

If the message is just plain, unformatted text, then the message body is just that end of story.

However, if the message has attachments or is formatted (i.e. uses HTML to make it pretty), then MIME comes into play. MIME provides for dividing the message body into parts and the leading lines of each part describe the format and content of the part. This is the second level of information encoding.

MIME is quite simple to understand. The message headers have a MIME boundary declared which is a bunch of characters that are fairly unique and unlikely to occur in the message body otherwise. These characters are used as a dividing line between each part of the message.

Following the boundary at the beginning of each part are some more lines containing colons. The key one of these is the MIME type. It may be something like TEXT/HTML or IMAGE/BMP. Your software maintains a table of these matching the type of attachment with an appropriate program to read the attachment. If your computer does not have an entry for a particular MIME/TYPE then you won't be able to do much more than save it.

Here is and example boundary and its headers.
Content-Type: image/jpeg; name="5SHANE.jpg"
Content-Transfer-Encoding: base64
Content-Disposition: inline; filename="5SHANE.jpg"

In the bad old days communications between computers was only 6 or 7 bits while computers where using 7 or 8 bit character sets. Thus, there needed to be a way of taking 7 ir 8 bit data down to 7 or 6 bits. There are a variety of encoding schemes that convert 8 bit data of any kind down to 6 bits - essentially the letters and numbers and a few characters. There are a variety of schemes to do the data reduction and the MIME headers for the part tell which one is used. This is the third level of information encoding.

binhex is just one of these schemes. It remains popular in the unix world and MAC worlds. Many PC's can't hack it. I would not recommend its use if you want a wide audience. In a recent inventory of 1086 pieces of email containing 4678 attachments i found it was not used.

base64 is a more universal encoding scheme and if you can configure your email program to use it, you should.

Quite frankly if your email program makes you worry about any of the above file formats then you should find a new email program.

Finally we get to the level you should be concerned about and that is the file format. It actually can constitute two levels depending on your choice.

You may have reason to zip all your files together and send them as one. If you are sending text or certain image formats this can result in some space savings. If you are saving JPG'sthen very little additional compression is possible. Many users these days will not open zip files because of all the malware running around that is disguised this way.

So we finally get to the level of the individual file. Here some thought is indeed required. You must understand what recipient is going to do with it and what software they have available. If you want to communicate with the Windows world do not send any file that contains a resource fork. If you want the end user to be able to edit an image then either send a BMP formatted file or one of the native formats of a common image editing program. Do NOT send a JPEG as they inherently have at least some information loss.

So some thought is required in communicating with a large audience. But I would suggest that it lies mainly in your choice of an email program that understands how to send binary files of any type to Windows world. If you do that then your recipient should be able to save the file to their hard drive and if they have the appropriate software open and use it.

A note about AOL

The use of AOL software at either end can complicate matters. The latest release of AOL has been known to produce MIME boundaries that are not comprehended by some receiving email programs. There is also the complication of it creating zip files which are now held in a lot of disrepute. Finally AOL is the source of ART files which are quite difficult for the rest of the world to hack.


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