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
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:
- Save screenshot to file
- Compose mail
- Click "Attach"
- Browse to saved file
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
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.