sendmail, 4th Edition

Recover from a Full Queue

When a queue directory is exceptionally full, you will likely notice the problem only when performance on your queue-handling machine becomes unusually sluggish. By that time, however, a drastic measure, such as rebooting the server, might be the only cure. Clearly, early detection is desirable.

Early signs that a queue is filling can be seen in the logging messages that sendmail produces. You can develop scripts that watch for lines such as these:

Dec 13 10:27:53 your.domain sendmail[642]: grew WorkList for /var/spool/mqueue to 2000
Dec 13 10:29:05 your.domain sendmail[642]: grew WorkList for /var/spool/mqueue to 3000
Dec 13 10:34:31 your.domain sendmail[642]: grew WorkList for /var/spool/mqueue to 4000
... etc., to:
Dec 13 12:40:22 your.domain sendmail[642]: grew WorkList for /var/spool/mqueue to
29000
Dec 13 12:42:50 your.domain sendmail[642]: grew WorkList for /var/spool/mqueue to
30000

Here, the WorkList refers to the number of messages preread so far. By searching for unusual sizes, you can determine when a queue is about to overfill.

Another technique is to run the mailq command to observe the total number of messages queued across all queues:

% mailq -OMaxQueueRunSize=0 | tail −1        ← V8.7 through V8.11
                           Total Requests: 34190

% mailq -bP                                  ← V8.12 and later
/var/spool/mqueues/q.1/df: entries=34190
                Total requests: 34190

For V8.7 through V8.11, the MaxQueueRunSize=0 allows mailq to run swiftly, regardless of how deep the queue or queues might be. Without that ...