Electronic mail, commonly called email, allows digital messages to be exchanged between an author and recipients. Early email systems required both parties to be online simultaneously, but modern email is based on a store-and-forward model where messages are sent and stored on servers until the recipient connects. Major advantages of email include near-instant delivery, very low or no cost of sending messages, ability to send messages to multiple recipients, and capability to attach digital files of any type. However, email can also create increased workloads if not managed properly and does not guarantee highly secure transmission of sensitive information.