How to reconcile discrepancies between ESP and third-party data?

Discrepancies occur because tools measure differently. ESP sees sent messages; third-party tools may see delivered or rendered messages. Timing differences affect counts. Definition variations cause different categorizations.

Reconciliation process: understand each tool's methodology, identify where measurements diverge, determine which source is authoritative for your purpose, and document known differences rather than trying to force agreement.

Practical approach: use ESP data for operational decisions (what you sent), MBP tools for reputation assessment (how you're perceived), and third-party tools for validation and gap-filling. Accept that perfect reconciliation is impossible; focus on consistent methodology within each purpose.