Most exchanges are text-only.
However, some services allow attachments. AOL first popularized instant messaging and, with its large membership, is likely to be the most popular service for some time to come. An Open Source alternative to AOL's instant messaging is called Jabber . An attempt to send an IM to someone who is not online, or who is not willing to accept IMs, will result in notification that the transmission cannot be completed. If the online software is set to accept IMs, it alerts the recipient with a distinctive sound, a window that indicates that an IM has arrived and allowing the recipient to accept or reject it, or a window containing the incoming message.