sendmail, 4th Edition

The Data (Message Body) File: df

All mail messages are composed of a header and a body. When queued, the body is stored in the df file.

Traditionally, the message body could contain only characters that had the high (most significant) bit turned off (cleared, set to 0). But under V8 sendmail, with a version 2 or higher configuration file (The V Configuration Command on page 580) the high bit is left as is until delivery (whereupon the F=7 delivery-agent flag, see F=7 on page 764, determines whether that bit will be stripped during delivery).

Because the message body can contain sensitive or personal information, the df file should be protected from reading by ordinary users. If the queue directory is world-readable, the TempFileMode option (TempFileMode on page 1097) should specify minimum permissions (such as 0600) for queued files. But if the queue directory is protected by both narrow permissions and a secure machine, the TempFileMode option can be relaxed for easier administration.

There is currently no plan to provide for encryption of df files. If you are concerned about the privacy of your message, you should use an end-to-end encryption package or an encrypting filesystem (not discussed in this book).