A Matching ID is a unique identifier assigned to each mailing that we use to track and report on your email.  

Setting up a Matching ID 

Matching IDs are automatically generated for your mailings by Salesforce Marketing Cloud.  The Matching ID is a combination of your MID number plus the Campaign ID (e.g. 4738271_3784832). 

No further work is required. 

When is a Matching ID needed? 

When you open a support ticket for issues related to seeded campaigns in Return Path Platform, include the matching ID(s) for all affected mailings in your issue description. It helps the support teams identify your issue quickly and aids them in troubleshooting.