Each release of
offers more and better ways to handle
queue problems. They are mostly implemented as options.
Section 34.6.2, "The Queue"
lists all options
that affect the queue. Of special interest are the new
Whenever you upgrade to a new
release, be sure to
for that latest information about new ways
to solve queueing problems.
The queue directory should never be shared among machines. Such sharing
can make detection of orphaned locks impossible.
Bugs in network locking daemons can lead
to race conditions in which neither of two machines can generate a queue identifier.
In old versions of
it was possible for an
file to be left in place even
though its corresponding mail message was not being processed.
Such spurious files prevented the message
from ever being delivered unless they were removed by hand. Spurious lock
files could be detected by watching the
Homespun programs and shell scripts for delivery of local mail
can fail and lose mail by exiting with the wrong value.
In the case of a recoverable error (a full disk, for example)
they should exit with EX_OSERR or EX_TEMPFAIL.
Both these exit values are defined in
cause the message to be requeued.
(2) into its queue directory,
you should avoid removing and recreating that directory while the
daemon is running. When processing the queue,
tries to read the queue directory by doing
(3) of the current directory. When the queue
directory is removed,
fails that open and
(3)'s the following warning:
orderq: cannot open "/usr/spool/mqueue" as ".": No such file or directory
Under a few old versions of
a bug in handling the queue could cause a message to be lost when
that message was the last in a queue run to be processed. This, among
other reasons, is good cause to always make sure you are running
the latest version of
program assumes that only it and other trusted
programs will place
files into the queue directory. Consequently, it trusts everything
it finds there. The queue directory
be protected from
other users and un-trusted programs.
If the queue directory is on a disk mounted separately from
, be certain to mount that disk
daemon. If you reverse these steps, the
(2) into the queue before
the mount. One effect of the reversal is that incoming mail will use a different
directory than outgoing mail. Another effect is that incoming queued
mail will be invisible. Yet another effect is that the outgoing queue
will never be processed by the daemon.