In the background, bxp generates is managing 10 data fields. When you send the email and the code is replaced in the body of the email. * EFU - CDAId is set to the CDA of the current record* EFU - CCLId Out, will log the CCL Id of the interaction that sent the email* EFU - DateTime Out will record the date and time the email was sent* EFU - Lock Key will be set with a generated unique code in The key is made up of : FormId_CDAId_CCLId_CDDId_LockKey When the receiving page gets this code, it is able to work out exactly what has to be done. If someone uploads a document, the following changes:* EFU - CCLId In is set to the CCL created for the upload* EFU - DateTime In is set to the datetime of the CCL* EFU - FileType is set* EFU - OldFilename is the name of the file as the user supplied it* EFU - NewFilename is set as per the bxp file management name* EFU - Lock Key is wiped to acknowledge the document is now uploaded So with the lock key now blank, the URL no longer works and the external user cannot interact with the LockFieldupload any more.