Retention notification settings include:
Whether to send warning notifications to retention administrators and/or users (file owners).
Whether to send deletion notifications to retention administrators and/or users (file owners).
Number of days to start warnings before the rule goes into effect.
By default, retention notification settings are taken from site level options, but they can be overridden for selected definitions.
Warning notifications are aggregated and sent once daily.
Deletion notifications are sent on each cycle (as defined in site options) when files are deleted.