Produce bounce message when Sendmail fails

Question

I'm trying to receive a bounce mail message when an outgoing message cannot reach smtp external server (due to my local internet connection problems).

I send emails using: mutt (compose) - procmail - esmtp (in place of sendmail) - GMail smtp server

When my connection is down and gmail smtp cannot be reached, I need to be alerted with a bounce mail from my email local system.

Is procmail the right "link in the chain" to set up to obtain this behavior? How configure it for bouncing?

EDIT:

.muttrc:

set sendmail="/usr/bin/formail -s /usr/bin/procmail -t -m /home/$myuser/.procmailoutrc"

.procmailoutrc:

MAILCONF=$HOME/.mail
LOGFILE=$MAILCONF/procmailout.log
LOGSENDMAIL=$MAILCONF/esmtp.log 
[...]
:0
* ^From.*address@gmail
{
        :0c:
        address@gmail
        :0
        | formail -I 'From ' | sendmail -v -t -X "$LOGSENDMAIL"
}

esmtprc:

identity address@gmail
        hostname smtp.gmail.com:587
        username "address@gmail"
        password "*"
        starttls required
        helo "*"
mda='/usr/bin/formail -a "Date: `date -R`" | /usr/bin/procmail -d %T'`

Since I found following error:

"SMTP server problem Temporary failure in name resolution"

written in $LOGFILE and not in $LOGSENDMAIL, I thought procmail was able to manage this returned error and send a "delivery failed" message to my mailbox.

As you can see in my config, mboxes name is the same of the real email address...

Answer 1

You are redirecting the standard output from sendmail to the log file, but standard error is not redirected, and so ends up in the Procmail log file.

I would imagine that sendmail sets a suitable exit code, and that you can simply generate a local bounce message when it fails if you want to.

This is becoming complex enough that I would create a separate script, although the code could probably somehow be inlined to your .procmailout as well.

#!/bin/sh
t=$(mktemp -t sendout.XXXXXXXXXXXX) || exit
trap 'rm -f "$t"' EXIT
trap 'exit 123' HUP INT TERM
formail -I "From " >"$t"
sendmail -v -t -X "$@" <"$t" && exit

# If we reached here, it's a failure
rc=$?
( printf "To: $USER\nFrom: MAILER_DAEMON\nSubject: Bounce\n\n"
  printf "The following message failed to send.  So sorry.\n\n"
  cat "$t" ) | sendmail -oi -t
exit $rc

You could send this script as sendout somewhere in your PATH (make sure it's in Procmail's PATH, too) and call it like

:0
| sendout "$LOGSENDMAIL"

The normal mode of stock Sendmail in case a message cannot be delivered immediately is to queue the message and report a temporary failure after a few hours, then retry until around a week has passed, then return the message as undeliverable if it still could not be delivered. I'm not familiar with esmtp but it sounds to me like maybe the default behavior of Sendmail (and thus in some configurations Postfix, Exim, etc) would perhaps be to your liking, so maybe simply switch to one of those (if esmtp can't be configured to behave similarly) and avoid creating your own solution.