We use sendmail in our mail server and today I saw an error message in /var/log/maillog, saying "timeout waiting for input from local during Draining Input".

I also saw that sendmail failed to deliver that mail (of size 5.9M).
I already google searched the web for this problem happening from time to time. There were only a few mentioning this problem, and some say it is actually timeout, some say it is a sendmail bug.

Since it was an important mail, I would like to recover it, if possible:

I looked into the mailspool, and I saw a file in the mailpool that has about the same size and creation time as the time of the failure, and also an other file the creation time of which is the same.
The first file in the mailspool seems to contain the body, and the second file seems to contain the header of the mail.

My questions are:
- can I make sendmail deliver the message that seems to be still sitting in the mailspool undelivered? ("sendmail -q" left it there)
- how to get rid of these timeout problems?

In the meantime I could recover the message by simply appending the two mailspool files to my mailbox and deleting some control characters in them. It now seems to be OK.

However, I am still curious what causes the timeouts.

I use procmail rules to apply some filter conditions to the body of mails and also pass thems through spamassassin and a mail scanner.
However, sendmail delivered 6 times bigger mails successfully before...
This problem exteremely often happens to mail messages sent by cron on the regular backup (zipping up) of many large files.

How is the email being generated in the script? Is it something like "start email, backup files, append results"?

The script itself does not generate any mails.
But it is run as a cron job, and cron automatically generates mails that contain the standard output of the jobs, if the mailto variable is not emptied in the crontab.

I am, however, not very annoyed by loosing these cron-generated mails, I only mentioned it here, because this is the only case when I always have the said error message, and maybe this helps to find out the reason.

I am rather annoyed about the fact that this sometimes happens to normal mails, too.
More surprising that these mails seem to be received fully by sendmail, but they sit in the mailspool undelivered forever, once such a timeout occured.