Recall message for a mail with 1000 recipients fails, it works for a smaller number of recipients or a little group. Message recall is based on the MessageID. If you issue a recall against a message, it will attempt to retrieve that MessageID from all recipients who received it. However, the Notes client will split the message for large numbers of recipents and they will have various MessageIDs.
ER is to handle message recall for email with large numbers of recipients.