How Are Messages Retried?

April 28, 2017 Contributors

Both SparkPost and SparkPost Enterprise employ the same settings for message retries, including message expiration settings (i.e., the maximum amount of time we will retry a message before we fail it for max attempts) and retry intervals, which is the time between successive delivery attempts.

Messages that fail delivery with a non-permanent failure code returned by the receiving MTA will continue to be retried from the delayed queue until the message is either:

  1. Successfully delivered.
  2. Receives a permanent failure error code back from the receiving MTA.
  3. Reaches the message expiration time, at which point SparkPost will automatically fail the message.

Retry Interval Logic

SparkPost and SparkPost Enterprise employ an exponential back-off scheme for retrying messages that are sent to the delayed queue and they are:

  • On the first failure the message is sent to the delayed queue and retried 20 minutes later.
  • On the second failure, the retry interval doubles to 40 minutes.
  • On the third failure, the retry interval quadruples to 80 minutes.
  • On the fourth failure, the retry interval multiplies by eight, to become 160 minutes.

This process continues until the message is delivered, or the message expiration timeout is reached, whichever comes first.

Message Expiration

The message expiration setting is 72 hours, which is the maximum amount of time a given message can be attempted before it will automatically fail.