3.1.3.1 Scope of the Search for Active Reminders
One of two approaches is typically used to specify the scope of the search for active reminders in the reminder queue: minimal reminder domain or full reminder domain.
Clients SHOULD<4> use a full reminder domain scope strategy. Using multiple clients that use different scope strategies to access the same mailbox is not recommended.
Using multiple clients that use different reminder domains can lead to inconsistent reminder signaling behavior. For example, different overdue reminders might signal in different clients, which can lead to missed reminders in the client with the smaller reminder domain.
Clients that use a full reminder domain scope strategy MUST ensure that the piReminderUpgradeTime property (section 2.2.3.1) is set. If the piReminderUpgradeTime property does not exist, the client MUST set it. The value SHOULD correspond to the current local time to reflect the time of upgrade to the expanded scope strategy of the newer client. The piReminderUpgradeTime property SHOULD<5> be set only once. If the value of the piReminderUpgradeTime property is already set, it SHOULD NOT be changed because it represents the first time an "upgraded" client was used.