Backoff, urgentbackoff, normalbackoff, nonurgentbackoff, ipbackoff Channel Options

Delivery retry intervals
Backoff options specify the frequency of message delivery retries when messages aren&#x27;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   channel option. Delivery will fail if successful delivery cannot be made within the time allowed by the last  channel option setting.

Interval values use ISO 8601 periodic time syntax: P&#x5b;yearsY&#x5d;&#x5b;monthsM&#x5d;&#x5b;weeksW&#x5d;&#x5b;daysD&#x5d;&#x5b;T&#x5b;hoursH&#x5d;&#x5b;minutesM&#x5d;&#x5b;secondsS&#x5d;&#x5d;  ,  ,  ,  ,   ,   and   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  channel option sets the retry intervals for urgent messages,   sets the retry intervals for normal priority messages, and   sets the interval for non urgent messages. sets the retry intervals for all messages regardless of priority.

Additionally, as of MS 8.0.2.3, an additional  option is provided to set backoff times for messages that have been placed in IP backoff mode. The ability to set ipbackoff values on a per-domin basis is also provided by the ipbackoff smartsend parameter.

The default intervals between delivery retry 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 ip: 60, 120, 120, 240, 240, 240, 480 Note that setting the various options on the defaults channel can be used to override these built-in defaults, as opposed to having to set the options on every channel with an associated queue in the configuration, e.g., msconfig&#x3e; set channel:defaults.backoff "PT30M PT1H PT2H PT4H" Also 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   setting; see the discussion of MTA message transaction log file   " " records.

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

See also:
 * notices Option
 * ISO 8601 P format
 * mtpriority_policy MTA Option
 * ims-ms channels
 * LMTP client TCPIP channels
 * ims-ms channel error messages
 * MTA transaction log entry format
 * Processing control and job submission channel options
 * Channel options