Email Validation and Deliverability API

We run a growing sign-up flow and a marketing list that keeps filling up with typos, dead mailboxes, and throwaway addresses. Bounces are hurting our sender reputation, and I want to stop the problem at the source. I am hiring a developer to build an email-validation and deliverability service exposed as a clean HTTP API. The core job is to take any address and tell me, quickly and reliably, whether it is worth sending to. That means real syntax parsing, domain and MX record checks, and a careful mailbox probe that confirms whether the inbox actually exists without getting our own IP blacklisted.

Beyond the single-address check, I need bulk list cleaning. I should be able to upload a list, have every row processed, and download the results with a clear verdict and a numeric quality score for each entry. The service must detect disposable and temporary domains, catch-all servers, and role addresses such as generic team or department inboxes, because those behave differently and I want to route them separately. Every response should be structured JSON so we can wire it into our own dashboard and CRM, and it needs to be fast enough to run inline during registration without making users wait. Please keep secrets and API keys out of the code and document the endpoints properly.

This is strictly about validating and cleaning existing lists. It is not a newsletter builder, not a template designer, and not a push-notification tool. If you have built verification or antispam pipelines before, show me examples and tell me how you handle greylisting and rate limits.

— Single-address check: syntax, domain, MX, mailbox existence
— Detection of disposable, catch-all, and role addresses
— Bulk list upload with per-row verdict and quality score
— Structured JSON API with keys, rate limits, and docs
— Sensible handling of greylisting to avoid false negatives