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NotificationType.PreviousWatermark Property

The PreviousWatermark property gets or sets the watermark of the latest event that was successfully communicated to the client for the subscription.

Namespace:  ExchangeWebServices
Assembly:  EWS (in EWS.dll)

public string PreviousWatermark { get; set; }

Property Value

Type: System.String
The PreviousWatermark property returns a string value that contains the last event that was successfully communicated.

The PreviousWatermark property is useful to the client in determining the last successful notification. For example, if a subscription has three events with watermarks 1, 2, and 3, and the next notification is sent with a PreviousWatermark value of 3, the client can compare this value to the Watermark value of the last notification received. This enables the client to ensure the continuity of events.

For push clients, the PreviousWatermark is compared to the local, client-side last known watermark. If the values are different, the client has missed an event notification and should reestablish a subscription by using the latest local watermark. For example, if a push client receives three events for a subscription with watermarks 1, 2, and 3, and the next notification includes a PreviousWatermark value of 5, the client has missed at least one notification and should create a new subscription, passing a 3 as the watermark.

For pull clients, the value of PreviousWatermark will be the same as the Watermark that is included by the client in the GetEvents call.