Mail.app, pasted graphics, and Windows recipients

[Draft]

Summary

When composing in Mail.app:

• if you attach a file, its format is preserved
• If you paste a screen capture, some capture formats will be translated to TIFF
• Some Windows users cannot view TIFF mail attachments
• This behavior seems to apply to other OS X applications as well

Here's a table showing how Mail.app translates pasted graphics, under Mac OS X 10.4.9:

Screen Capture	Pasted Format
GIF	TIFF
JPG	TIFF
PDF	PDF
PNG	PNG
TIFF	TIFF

Gory Details

If I paste screenshots into my Mail.app messages, some Windows recipients cannot see those screenshots. When sending to these recipients I have to use a much more tedious process:

1. Save screenshot to file
2. Compose mail
3. Click "Attach"
4. Browse to saved file

Others are dealing with the same problem. Witness this thread at macosxhints.com.

Is the problem that the pasted graphics are set to display inline? (Content-Disposition: inline) No. No matter how I make an attachment, whether through pasting or through the Attach button, Mail.app always sets Content-Disposition to inline. And Windows users can see some attachments.

Is there anything relevant in ~/Library/Preferences/com.apple.mail.plist? Not as far as I can tell.

I have changed my default screen capture format, following the instructions in this macosxhints article:

    defaults write com.apple.screencapture type format
    killall SystemUIServer

My format is set to jpeg. That seems to be the problem. Mail.app translates pasted JPEG images to TIFF. Attached JPEG images retain their format.

I'm not sure about the reasons for this, but Preview.app seems to confirm the following weirdness: If you do a screen capture to the clipboard, some formats such as JPG get converted to PICT. If you do the screen capture to a file, then the format you specify is the format used in the capture file.