If you install Reaper with the "portable install" option selected, it places the entire program and associated configuration, themes, hotkey settings, etc, into a single directory (rather than the traditional method of installation, which is not fully self-contained.)
This has a few advantages:
Stripping, sanitizing, or otherwise translating filenames when copying or moving from one file system to another with different rules for file names can be a pain. I had to copy many GB of files off a friend's dead Mac iBook G4. Macs use the HFS+ file system, and while ext3/4 actually allows a lot of the same odd characters, you don't see them as often in an OS where people use command lines, and anyway I was copying to a FAT32 partition.
So, your outgoing messages are failing SPF, or your own SPF verifier is failing message for no good reason, and you want to figure out why? It might be the DNS of the sending domain.