Backoff, urgentbackoff, normalbackoff, nonurgentbackoff, ipbackoff Channel Options

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Delivery retry intervals (backoff, urgentbackoff, normalbackoff, nonurgentbackoff)

Backoff options specify the frequency of message delivery retries when messages aren't successfully delivered the first time. These options all accept a series of intervals as arguments. The first interval specifies the time to wait before the first retry, the second specifies the time to wait for the second retry, and so on. The last value given specifies the time to wait for all subsequent retries. Up to eight intervals can be specified. Deliveries are attempted for a period of time specified by the notices channel option. Delivery will fail if successful delivery cannot be made within the time allowed by the last notices channel option setting.

Interval values use ISO 8601 periodic time syntax:


years, months, weeks, days, hours, minutes and seconds are all integer values.

Note that all of the letters in the value must be written in upper case.

Separate interval settings are allowed for messages with different priority settings. The urgentbackoff channel option sets the retry intervals for urgent messages, normalbackoff sets the retry intervals for normal priority messages, and nonurgentbackoff sets the interval for non urgent messages. backoff sets the retry intervals for all messages regardless of priority.

The default intervals between delivery retries attempts in minutes are:

urgent: 30, 60, 60, 120, 120, 120, 240
normal: 60, 120, 120, 240, 240, 240, 480
nonurgent: 120, 240, 240, 480, 480, 480, 960

Note that the MTA has special handling of the case of problems delivering to some recipients of multi-recipient messages: in such cases, the failing recipients are eligible for another "immediate" delivery attempt without regard to *backoff setting; see the discussion of MTA message transaction log file "Z" records.

Note that ims-ms channels and LMTP client TCP/IP channels have special case handling that overrides normal backoff for the specific error condition of encountering IMAP_MAILBOX_LOCKED when attempting delivery to a Message Store user.

See also: