KB13227: How does MicroStrategy Narrowcast Server determine how many emails are generated in a service?

A Strategy Narrowcast Server service is made up of a publication, schedule, and subscription set.
 
During service execution, the subscription set is divided into segments. Within each segment, subscriptions with the same personalizations (preference and authentication objects) are further grouped together and treated as one.
 
Keeping the above in mind, consider the following scenario:
 

• ServiceA has a segment size of 10 and delivers content personalized on a prompt on the Region attribute.
• SubscriptionA, subscriptionB and subscriptionC belong to userA, userB, and userC respectively. None of the users have authentication objects defined.
• There are 3 subscriptions made to ServiceA where subscriptionA chose regionA, subscriptionB chose regionA, and subscriptionC chose regionC. Notice that the preference for subscriptionA = preference of subscriptionB.

Different Preference Objects
In terms of the number of emails created, the above service will generate 2 email bodies since within that segment subscriptionA and subscriptionB both chose regionA and subscriptionC chose regionC. Within a segment, Strategy Narrowcast Server will group subscriptions of like preferences and authentication objects.
 
Different Authentication Objects
If the original scenario is changed so that userA and userB have different authentication objects (their preference objects are the same but their authentication objects are different) then 3 email bodies will be generated.
 
Different Segments
If the original scenario is changed once again so that the service segment size is changed from 10 to 1, then each segment will contain a subscription. Since Strategy Narrowcast Server will group subscriptions of like preferences and authentication objects on a segment-by-segment basis, there will be 3 email bodies generated.
 
In conclusion, the number of emails Strategy Narrowcast Server generates is based on whether subscriptions:
 

1. Are in the same segment (number of segments/segment size).
2. Have the same preference and authentication objects within a segment.