Hello and welcome to the forum,
I put this topic in JCL map because I use XMITIP in JCL Cobol file.
There is no such thing as "JCL Cobol file" - you or your organization may find this meaningful, but within the IBM mainframe industry it has no meaning. You will do much better if you do not create terms to use - you need to use "standard" terminology.
I suspect someone moved it (i don't know who moved it) because it is not a JCL question. . .
Batch jobs submitted by a scheduling system, some online application, or manually all run with JCL. That does not mean any question about them is a JCL question. . .
To do what you want, specify multiple attachment files for the xmitip step.