When an SMS message cannot be delivered owing to temporary errors (for example, the SMPP server is not reachable), the email message is left in the delivery queue and retried again later. Unless configured otherwise, the Job Controller will not re-attempt delivery for an hour. For SMS messaging, that is likely too long to wait. As such, it is recommended that the backoff channel keyword be used with the SMS channel to specify a more aggressive schedule for delivery attempts. For example,
sms_mway port 55555 threaddepth 20 \ backoff "pt2m" "pt5m" "pt10m" "pt30m" notices 1 smpp.siroe.com
With the above settings, a redelivery attempt will be made at two minutes after the first attempt. If that then fails, then five minutes after the second attempt. Then ten minutes later and finally every thirty minutes. The notices 1 channel keyword causes the message to be returned as undeliverable if it cannot be delivered after a day.