The files that populate a queue directory are the qf, df, and xf files. The qf file (Section 11.11) contains envelope information and the message's headers. The df file (Section 11.2.2) contains the body of the message. The xf file (Section 11.2.7), when present, contains a copy of failed SMTP replies and other error messages generated during a delivery attempt.

If the SuperSafe option (SuperSafe) is set to true, all messages are placed in the queue prior to delivery. If that option is false (or interactive beginning with V8.12) only messages that fail to be delivered on the first attempt are placed into the queue. When a message is placed into the queue, the qf and df files are created. The permissions that the files get are determined by this QueueFileMode option.

The QueueFileMode option is declared like this:

O QueueFileMode=perms                configuration file (V8.12 and later) 
-OQueueFileMode=perms                command line (V8.12 and later) 
define(`confQUEUE_FILE_MODE',`perms')    mc configuration (V8.12 and later) 

Here, perms is the permissions that will be given to the created files. Those permissions are of type octal. The default is 0600 (if the real-user-id is the same as the effective-user-id), and 0644 otherwise. If the mode has the group-writable bit set (as in 0664), the umask(2) is set to 0002 (disallow world-writable permissions) just prior to the open(2) or creat(2), and restored to its prior value just after.

Be careful to supply only an octal value to this option. If you mistakenly give it a string (such as QueueFileMode=o+rwx), you will find your queue files being created with a mode of 000, and sendmail will be unable to read them.

In general, it is recommended that queue files be created with the narrowest permission possible. Unless you have a compelling reason to change the defaults, you should leave them as is.

The QueueFileMode option is not safe. If specified from the command line, it can cause sendmail to relinquish its special privileges.