Hi thomash82948276,
You can refer to broad log for previous communication history and exclude recipients based on that.
Assuming that you have multiple workflows inside a single campaign and you don't want to target those recipients already communicated by any workflow belonging to the campaign you can do something like following.
1. You have to run the workflows sequentially.
2. Fetch workflows belonging to same campaign, which are in finished state(using javascript would be an easy option).
3. Keeping recipient as filtering dimension use the following relationship to filter out recipients.
Recipients-> Broad log->Delivery->Workflow
Regards,
Deb