Hello,
Probably what you are looking is an EDM profile. With this method you can create a profile based on structured data.
Once done, instead of add it as detection, you would need to add as exception to the policy.
Check these links below for more details:
https://www.symantec.com/connect/articles/how-implement-exact-data-matching
https://www.symantec.com/connect/forums/dlp-edm
Admin guide also provides lots of info about it:
https://support.symantec.com/en_US/article.DOC9261.html
Best,
Morgado