The ALTMSG option allows you to change the message data set DDname that will be used for program-initiated applications. The default name is SYSOUT.
To use a different name, substitute it in place of cccccccc. The name may contain up to 8 characters. If the DDname specified by ALTMSG is not provided in the JCL for a program-initiated application, then MFX will use the DDname specified in the MSGDD option, if available.