[ACS] Target mapping called: External file, how to use it ?

[sangramg5524113]

My Client mentioned they had ‘done this before’ where they sent to records that don’t exist on nms:recipient. I’ve seen this done in ACC before but it’s not recommended.

I do see they have target mapping called: External file.  I don’t know how this is used or if it’s intended for this.  I am currently trying to test it but each time I use a template wit this mapping I get a blank screen so clearly doesn’t work.

Any ideas?