Apple has not documented .emlx. This page follows the open-source
emlx Python reader (its README and
emlx/emlx.py, read 2026-11-12), which credits Jamie Zawinski’s 2005
notes for the flag bits. Nothing here is confirmed by Apple.
Layout
- A first line holding the length of the message in bytes as a decimal number (the reader strips white space around it).
- The message: exactly that many bytes of an RFC 5322 message with its MIME parts and attachments.
- From there to the end of the file, an Apple property list with Mail’s information about the message.
Property list keys
The reader’s README shows the keys color,
conversation-id, date-last-viewed and flags,
followed by others it does not list. It decodes only flags, an integer
described below.
Flags
Bits counted from the least significant, in the order the reader decodes them. The reader drops an attachment count of 63, noting that it appears in some files without explanation.
| Bits | Meaning |
|---|---|
| 0 | Read |
| 1 | Deleted |
| 2 | Answered |
| 3 | Encrypted |
| 4 | Flagged |
| 5 | Recent |
| 6 | Draft |
| 7 | Initial (not yet downloaded) |
| 8 | Forwarded |
| 9 | Redirected |
| 10 to 15 | Number of attachments |
| 16 to 22 | Priority level |
| 23 | Signed |
| 24 | Junk |
| 25 | Not junk |
| 26 to 28 | Font size change |
| 29 | Junk level recorded |
| 30 | Highlighted in the message list |
| 31 and up | Not described; newer Mail versions use further bits whose meanings are not published |