User IDs across systems

Platforms other than Windows, UNIX and Linux® systems use uppercase characters for user IDs in messages.

To allow Windows, UNIX and Linux systems to use lowercase user IDs in messages, the following conversions are carried out by the message channel agent (MCA) on these platforms:
At the sending end
The alphabetic characters in all user IDs are converted to uppercase characters, if there is no message exit installed.
At the receiving end
The alphabetic characters in all user IDs are converted to lowercase characters, if there is no message exit installed.

The automatic conversions are not carried out if you provide a message exit on UNIX, Linux and Windows systems for any other reason.