A method of sending an email message having one or more attached files to a plurality of recipients allows customized treatment of each file as it is being sent to each recipient. Treatments may include different types of encryption, plain text transmission, security classification or user-defined treatments. The invention may be implemented in a client-server configuration with separate client and server programs or in a single integrated email program configuration for use on a single computer. The user is presented with a list of recipients, selects a recipient and then selects a treatment for each file to be used when that file is sent to the selected recipient. This process is repeated for each recipient and each file. A control file is generated by the client program, including the recipient information and the file treatment information for each recipient and each file. The client program sends a single copy of the email message, a single copy of each file and the control file to the server program. The server program reads the control file and prepares individualized emails for each recipient by applying the control file specified treatments for each attached file.
