A corporate action notification is the message by which an intermediary tells its clients that an event has been announced on a security they hold. Once corporate action event capture has produced a validated record, the custodian or depository identifies every account with a position or pending trade in the security and sends each one the event details: the event type, key dates, rate, the options on offer and the client's eligible balance.
Notifications pass down the chain from the central securities depository to custodians, then to investment managers and end investors. Between institutions they are usually sent as structured messages, traditionally the SWIFT MT 564 and increasingly its ISO 20022 equivalent. Updates are sent when terms change, and reminders are issued for events that need a corporate action election, quoting the intermediary's own election deadline.