Checkhandler can be used to spool messages. In this sample there are two servers both running Smstools3. Main server has lot of saldo on it's SIM and should be used to send most of messages. Application server has limited saldo and this SIM should be used only for administrative purposes and for backup purposes when a communication between the servers fails.

Main server runs a PHP script published in this post. It's stored as /var/www/send-xxyyzz.php, where xxyyzz is a simple code to protect this script. As the content of a folder is never shown, the script cannot be called unless it's name is known.

Application server has a checkhandler defined in the smsd.conf file:
checkhandler = /usr/local/bin/smsd_checkhandler

The application which uses another server to send SMS, creates a message files using an additional Send_thru header:

To: 358401234567

Hi there, this is a message from the Application.

The checkhandler code is:


tmp=`formail -zx "Send_thru:" < "$1"`
if [ "x$tmp" = "xMAINSERVER" ]; then


  FILE=`mktemp /tmp/send_thru_XXXXXX`

  to=`formail -zx "To:" < "$1"`
  messagebody=`sed -e '1,/^$/ d' < "$1"`
  urlsafe_message=`echo "$messagebody" | sed 's/\n/%0A/g' | sed 's/%/%25/g' | sed 's/&/%26/g' | sed 's/#/%23/g'`

  # https is used with a self-signed certificate:
  wget --no-check-certificate -t 1 --read-timeout=$rtout \
    "https://${SERVER}/${SCRIPT}?To=$to&Message=$urlsafe_message" -O $FILE  > /dev/null 2>&1

  # Check the result.
  if grep "OK." $FILE >/dev/null; then
    rm $FILE
    rm "$1"
    exit 2 # Checkhandler has spooled this message.


exit 0
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