Undeliverable messages are held in a given channel queue for specified amount of time before being returned to sender. In addition, a series of status/warning messages can be returned to the sender while Messaging Server attempts delivery. The amount of time and intervals between messages can be specified with the notices, nonurgentnotices, normalnotices, or urgentnotices keywords. Examples:
notices 1 2 3
Transient failure status notification messages are sent after 1 and 2 days for all messages. If the message is still not delivered after 3 days, it is returned to its originator.
Transient failure notifications are sent after 2, 4, and 6 days for messages of urgent priority. If the message is still not delivered after 8 days, it is returned to its originator.
Note that the RETURN_UNITS option in the MTA Options file allows you to specify the units in either hours (1) or days (0). The default is days (0). If you set RETURN_UNITS=1, then you will need to schedule the return job to run hourly as well to get hourly notices. When the return job runs every hour it will also roll over the mail.log* files every hour. To prevent the hourly rollover of the mail.log file, set the IMTA_RETURN_SPLIT_PERIOD tailor file option in the imta.tailor file to 24. Return job scheduling is controlled by the local.schedule.return_job configutil parameter. Note, however, that by default this command is run on a regular basis (see 4.6.2 Pre-defined Automatic Tasks).
If no notices keyword is specified, the default is to use the notices setting for the local, l, channel. If no setting has been made for the local channel, then the default is to use notices 3, 6, 9, 12.