Deliverability is mostly configuration. We set up and check the parts that decide whether a message arrives, and verify them against what the receiving side actually sees.
Gap reporting
What is missing from a universe, named rather than rounded away.
Source appraisal
Establishing where each field can come from, how current it is, and what it is permitted to be used for.
Count reconciliation
Producing the figure by the same route the final selection takes, so the two cannot disagree.
Send a file and we will report what share of it we can stand behind.