188.8.131.52 Estimating the Number of Changes
The client sends a GetItemEstimate command request to the server to get an estimate of the number of changes to SMS items for a given email folder. (An email folder is one that contains email messages.)
This operation on SMS items is supported only for the Inbox folder, the Outbox folder, and the Sent Items folder when protocol version 14.0 is used; it is supported for all email folders when protocol version 14.1 or 16.0 is used. Other protocol versions do not support this operation on SMS items.
The estimate of changes will include changes to SMS items for an email folder only if the request includes an airsync:Options block with the airsync:Class element ([MS-ASCMD] section 184.108.40.206.1) set to "SMS". A maximum of two airsync:Options blocks are allowed within a getitemestimate:Collection block, namely one for the default class of the given email folder and one for SMS items. The airsync:Class element MUST be set to "SMS" to indicate that the options apply to SMS items.
The GetItemEstimate command request is further specified in [MS-ASCMD] section 220.127.116.11.