The SMTP rules data set

You can override the default rules for header addresses by creating an SMTP rules data set. This allows you to customize the address transformations to the needs of a particular site. If you are customizing SMTP mail headers, this task is required.

The SMTP rules data set is pointed to by the //SMTPRULE DD statement in the SMTP cataloged procedure. The SMTP rules data set consists of:
Field definition
Contains the names of all header fields whose addresses are to be rewritten.
Rules definition
Contains the rewrite rules for the header fields.