There is a need to use wildcards within the NonMultipartAttachment.config file.
For example you would like to use *.box.com instead of upload.box.com to include all subdomains of box.com.

The file uses a substring match. 
If you specify “Host == .box.com”, it should match every message in which the Host contains “.box.com”.
Because it’s a substring match, the system could easily match on unintended messages, so it’s important to be as specific as possible.