The Send Adapter commits changes per message and per object. This means commits cannot span messages. Within a message, changes to an object are all committed together. To ensure changes are all or nothing, therefore, the strategy you need to use is one message per object.
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Try adding the setting PageSize="1000" to your query parameters. For example:
<ActiveDirectoryQuery><Directives WhereToBind="LDAP://CN=Users, DC=test, DC=com" Filter="(objectCategory=user)" SearchScope="onelevel" PropertiesToReturn="cn" PageSize="1000"/></ActiveDirectoryQuery>
By default Active Directory only allows for a single page of 1000 results. By explicitly setting this value multiple pages (and hence all results) are returned.
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