I have large CSV lists of addresses and I need a straightforward tool that tells me which emails will actually reach an inbox. The key requirement is deliverability testing; I’m not interested in simply catching typos—I want to know whether each address can really receive mail. Domain-level validation must be part of the logic. The script should check that MX records exist and that the domain is capable of accepting messages. If you have a proven, low-latency way to add additional checks (such as a lightweight SMTP handshake that stops short of sending a message) I’m open to it, as long as it doesn’t violate host policies or slow the bulk run noticeably. Workflow I have in mind: I drop a file (CSV or TXT) containing thousands of emails into a folder, run the program, and get a fresh file back showing Deliverable / Undeliverable status along with a short summary report. A simple command-line interface is fine, but if you prefer a minimal web front-end that lets me choose the file and hit “Validate,” that works too. The code should be clean, documented, and easy for me to host on a standard Linux VPS. Deliverables • Source code with clear comments • README covering setup, dependencies, and usage • Sample input file and the corresponding validated output • Quick guide on how to adjust timeout or concurrency settings for very large lists If you have questions about my environment or preferred language, just let me know—I’m flexible as long as the final tool is reliable and fast on bulk uploads.