harmon.ie is used to send links to SharePoint documents by email. If the location or the name of the document is changed, the link becomes inaccessible.
SharePoint links normally include the full path to the document and the document name.
SharePoint 2010 introduced the document ID feature and service, which is a site collection feature. When this feature is activated, it adds a Document ID property to all document content types and assigns a unique ID to every document uploaded to SharePoint.
The Document ID property is a URL in this format: http://<site URL>/_layouts/DocIdRedir.aspx?ID=J2W3DN6QF6XW-2-40. When this URL is clicked, search is used to find the document. This allows the URL to work even if the document has been moved to another location, or renamed.
harmon.ie can also produce persistent URLs to SharePoint documents, containing the document ID instead of full path. To enable this feature:
Note that if the document ID feature is disabled on the SharePoint site, a full path link is created even if the PreferDocumentIDs registry key is set to True.
When the Document ID feature is enabled, items that are returned by the site search do not include the Document ID property. As a result, when you drag and drop an item from the search results to an email, a regular link with the full document path is created, and not a link with the document ID.