Mixed Case Password support for external signon security was added in 15.0. It is part of the software and does not require any optional settings in IDMS.
There were PTFs related to mixed-case password support in 16.0 and 17.0 but there have been no problems reported on 18.0 or 18.5 or 19.0.
If RACF is set to support 'mixed' case passwords, then PRIOR to receiving the password from a SIGNON done from ENTER NEXT TASK CODE, IDMS will take exactly what the client entered on their VTAM terminal session. IDMS will then check to see if RACF is the security system and - if so - check to see if it supports mixed case passwords. If so, IDMS will send it to the external security system software exactly as entered. * Setting case to UPLOW is needed only if say, you have a map accepting the PASSWORD field. That field must accept lower case characters and not convert them into uppercase. Note here that the session must be set to a DCUF UPLOW. * If IDMS sees that RACF is not set to support mixed case passwords - then IDMS will force upper case when we call external security for the RACF password call. IDMS does that because RACF rejects passwords containing lowercase characters if RACF is not set to support mixed case.