Enable this policy setting to prevent the indexing of the content of e-mail attachments. If enabled, indexing service components ...

Enable this policy setting to prevent the indexing of the content of e-mail attachments. If enabled, indexing service components (including non-Microsoft components) are expected not to index e-mail attachments. Consider enabling this policy if you are concerned about the security or indexing performance of non-Microsoft document filters (iFilters). This policy is disabled by default.