Specifies the mailbox extension of the application to which you are connecting. This parameter corresponds with the -EXT parameter used when connecting using the Datanet Terminal manager. The mailbox extension is only used when connecting to CXI (GCOS8) subsystems, and will normally contain the LID (Logical ID). The mailbox extension string can contain up to 4 characters. Login to GCOS8 via CXI requires that the host mode be set to CXI. When you define a LID in TP8, one of the parameters is mailbox extension, usually set to be equal to the LID.