Mail.dat is a database standard developed by IDEAlliance (formerly Graphic Communications Association) to describe all aspects of a mailing. Mail.dat databases are used to communicate information to clients, between departments, and to the USPS via the PostalOne! program. In order to generate a valid Mail.dat database, you must first obtain a User License Code from IDEAlliance.

For more information on the specifics of the Mail.dat data interchange standard or to obtain the required Mail.dat User License Code, visit the IDEAlliance Web site. IDEAlliance offers a Mail.dat User Guide, technical specifications, and membership services, in addition to User License Codes.