Identification of protected content in e-mail messages

A method of controlling distribution of messages by identifying protected content in the body of e-mail messages, the method comprising:

• maintaining a database stored in memory, the database comprising content previously identified by a user as protected content, the protected content being associated with permission information specified by the user, the permission information specifying other users that have been authorized to access the protected content and other users that have been authorized to redistribute the protected content, wherein the protected content is not allowed outside of a private network absent an indication that both a sender and an intended recipient have been authorized to access and/or redistribute the content;
• intercepting an e-mail message addressed to at least one recipient by a sender;
• and
• executing instructions stored in memory, wherein execution of the instructions by a processor:
• extracts content from the body of the intercepted e-mail message,
• compares the extracted content to the protected content stored in the database in order to identify similarity between at least a portion of the extracted content and the protected content stored in the database, wherein the identified similar portion is not identical to the protected content, and wherein the comparison uses one or more detection techniques to identify the similar portion of extracted content and the one or more detection techniques include determining that the portion of extracted content is more likely to match protected content when misplaced non-alphabetic characters are present in the portion of the extracted content than when misplaced alphabetic characters are present in the portion of extracted content,
• determines that the extracted content includes protected content based on the identified similarity to protected content stored in the database,
• determines that the sender is authorized to redistribute the protected content and the at least one recipient is authorized to access the protected content as specified by the permission information associated with the protected content, and
• allows the message to be transmitted outside of a private network behind a security appliance based on the determination that the content extracted from the body of the e-mail message includes protected content and the determination that the sender is authorized to redistribute the protected content and the at least one recipient is authorized to access the protected content.