Validate 500k Email List

I'm looking for a professional to validate my email list of approximately 500,000 entries. The validation process should cover syntax checks to identify invalid formatting, domain checks to ensure the domain exists, and mailbox verification to confirm the emails can receive mail.

The list is currently stored in a text file, and after validation, any invalid email addresses should be flagged or highlighted directly within the file. I need this task completed within 24 hours. If you have the expertise and tools to handle this efficiently, I'd love to work with you on this project.