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Determine if the email address is "public"

I would like to determine if the email address comes from a public provider or from an established business. I believe that publicly available email addresses are as follows:

  • Open mail service providers such as gmail, hotmail and yahoo.
  • Anonymization services, such as email client or dispatch.

I know that there is no reliable way to do this, and obviously, any list-based solution will require constant updates.

Is there a public list or .NET library that can do this for me?

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Are there really many free email providers? I would go with a blacklist solution.

For example, mark everything on this wikipedia list as free (hell, I think gmail / hotmail / yahoo / aol coverage will cover a huge% of users anyway). Then, if you receive more than 2 (or a higher number, if your site has high bandwidth) registrations from the same email domain, it notifies the administrator about the domain check to see if it needs to be added to the black list.

I would suggest that there are much more reliable ways to discover business customers. For example, in Australia, you can simply ask for ABN and then verify that it is valid. Are you ready to punish a small business that does not have email and just use a shared @gmail account?

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Here is a link to the SpamAssasin spam list: http://svn.apache.org/repos/asf/spamassassin/trunk/rules/20_freemail_domains.cf .
I believe checking this list is a good start.

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You might want to talk to the Better-Business-Bureau ( http://www.bbb.org ) and see if they provide any feed or API. I quickly looked at their website and could not see anything obvious, but it would be such an organization in which I would like to start if I wanted to know the domain names belonging to established enterprises. They have a search form on their website by email ( http://www.bbb.org/us/Find-Business-Reviews/ )

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