Match My Email does use API calls provided to each Salesforce ORG. Generally, organizations are allocated 100,000 API calls per 24-hour period plus extra API calls for each licensed user. Professional and Enterprise licenses grant an extra 1,000 API calls per 24-hour period while Unlimited and Performance licenses grant 5,000 extra API calls per licensed user. The official SFDC developer cheap sheet can be accessed at this URL: https://developer.salesforce.com/docs/atlas.en-us.salesforce_app_limits_cheatsheet.meta/salesforce_app_limits_cheatsheet/salesforce_app_limits_platform_api.htm
MME uses between 1 and 5 API calls per email in processing. More precisely, 1 call is used for “No Match”emails and 2-5 calls for “Match” emails. API calls are used for finding a match, uploading email body text, uploading attachments. It is very unlikely that Match My Email would consume enough API calls to cause an overage with a temporary lock-out condition. No verified API call overage/lock-out due to Match My Email has ever been reported to MME Support.
In order to check the number of API calls consumed by application for your Salesforce organization please visit: Reports | Administrative Reports | API Usage for last 7 days
For assistance or questions, please contact firstname.lastname@example.org.