Best Practices for Gathering Emails and Conserving Credit Usage in the Waterfall Email Enrichment Process

'Waterfall Email Enrichment' Curious about what others are doing to gather emails while keeping credit usage low. When running the email waterfall I have 3 or 4 providers and a validation tool on. Sometimes each provider gives back the same email and the validation tool denies it each time. This is costing way more credits than I would like. Wondering what creative ways people are navigating this?