A method of configuring a system for providing notification of a new email received at a user's mailbox stored by a first mail storage system for retrieval by a second mail storage system. The method comprises configuring a mail sender to send a notification email to the second mail storage system comprising data to notify the second mail storage system of the new email, receive a rejection message from the second mail storage system, and interrupt the sending of further data of the notification email in response to the rejection message, wherein the receipt by the second mail storage system of the notification email triggers the second mail storage system to retrieve the new email from the first mail storage system.