Beginning with V8.12 sendmail, it is possible to
split envelopes for more efficient delivery. When
sendmail splits an envelope, the new
qf file will share a df file
with the prior qf file. But to ensure that each
qf file has it own df file,
sendmail creates a hard link to make a copy of
the df file. That way the old
qf file uses the old df
file, and the new qf file uses the new
df file. The two df files
are the same because they are hard-linked together.
A problem arises when the two qf files are saved
on two different disks. Because it is not possible to hard-link
across disks, the new qf file is put on the new
disk, but the new df file is left on the old
disk. That way an efficient hard link can still be made, but now the
new qf file and its new df
file are on different disks.
The d qf-file line was
introduced to allow a qf file to find its
corresponding df file when that
df file is on a different disk. Whenever a
qf file has a corresponding
df file on a different disk, that
qf file will contain a d line
that looks like this:
d/path
The /path must be the full pathname of the
directory that contains the df part. If
/path is missing, or is not a directory
that was set in the configuration file, the following error is logged
and the qf file is considered bad, and marked as
such (Section 11.5):
Losing qf file: bogus queue file directory