I am a seller on amazon and they don't give customer real email so I use datafinder to extract real emails using customer full name, address, zipcode, etc. on datafinder. It's a good what to extract real email and they also offer other services like interest and social media so you can better target your mailing list. so far datafinder.com is the most affordable option for email append service that I found. Open to ideas, I think it'll be awesome to link it up to mautic.