Method and system for processing messages based on instant messaging, client and server

The invention provides a method and system for processing messages based on instant messaging, a client and a server. The method includes the following steps: a sending end receives instant messages input by a user and priority information selected by the user, and the instant messages and the priority information are sent to the server; the server judges whether a receiver of the instant messages is online; if the server judges that the receiver of the instant messages is not online, the priority information of the instant messages is analyzed; and if the priority information is of a preset level, the server sends the instant messages to the receiver through short messages and/or an online social website. By means of the method of an embodiment, different sending strategies are adopted for sending the instant messages according to the priority information, the method has pertinence, the instant messages with a high priority level can be sent to the receiver through the short messages and/or the online social