[Chapter 23] 23.7 Process Alternate Queues

23.7 Process Alternate Queues

The sendmail program provides the ability to use queue directories other than the one listed in the configuration file's QueueDirectory (Q) option (see Section 34.8.48). Other queue directories can be used to solve an assortment of problems. One example is a site being down for an extended period. When a lot of mail is sent to such a site, messages collect in the queue and eventually start timing out. By moving those messages to a separate queue directory and processing it at a later time (when that site is back up), unnecessary bouncing of mail can be prevented.

Note that the QueueDirectory (Q) option is not safe. If its value is changed by anyone other than root, sendmail runs as an ordinary user.

23.7.1 Handling a Down Site

If a site is down, messages to that site can collect in the queue. If the site is expected to be down for a protracted period of time, those queued messages will begin to time out and bounce. To prevent them from bouncing, you can move them to a separate queue directory. Later, when the down site comes back up, you can process that separate queue.

To move the affected messages to a separate queue, you may use a Bourne shell script like the following:

#!/bin/sh
set -u
QUEUE=/var/spool/mqueue
NEWQ=/var/spool/newqueue

if [ ! -d $QUEUE ]
then
        echo "${QUEUE}: Does not exist or is not a directory"
        exit 1
fi
if [ ! -d $NEWQ ]
then
        mkdir -p $NEWQ
        if [ $? -ne 0 ]
        then
                echo "${NEWQ}: Can't create"
                exit 2
        fi
fi
find ${QUEUE} -type f -name qf* -print |\
while read QF
do
        IDENT=`echo $QF | sed -e "s,^${QUEUE}/qf,,"`
        grep "^R" ${QUEUE}/qf${IDENT}
        echo -n "move ${IDENT}? (y/n) "
        read answer
        case $answer in
                [nN]*)  continue;;
                *)      ;;
        esac
        mv ${QUEUE}/*${IDENT} $NEWQ
        if [ $? -ne 0 ]
        then
                echo "Move failed"
                exit 3
        else
                echo "Move succeeded"
        fi
done
/usr/lib/sendmail -OQueueDirectory=${NEWQ} -bp

This script creates a new queue directory, $NEWQ, if it doesn't exist. It then prints the recipient list for each qf file in the queue (the grep(1) in $QUEUE) and asks whether you want to move that file. If you answer yes, all the files that compose the queued message are moved into $NEWQ. After all the messages have been moved, the contents of $NEWQ are printed using the QueueDirectory (Q) option:

% /usr/lib/sendmail -OQueueDirectory=${NEWQ} -bp

When the down site comes back up at a later time, the messages that have been saved in $NEWQ can be delivered by running the following command by hand:

% /usr/lib/sendmail -OQueueDirectory=/var/spool/newqueue -OTimeout.queuereturn=99d -q

The -oTimeout.queuereturn=99d causes the time to live in the queue to be extended to 99 days. This prevents the held mail in ${NEWQ} from wrongly bouncing when you try to deliver it.


23.6 Cause the Queue to Be Processed		23.8 Pitfalls