Identify if an email address is 'public'

Question

I would like to identify if an email address comes from a public provider or is from an established business. I consider public email addresses to be things such as:

• Open email service providers, such as gmail, hotmail and yahoo.
• Anonymization services, such as mailinator or dispostable.

I'm aware that there is no foolproof way to do this, and obviously any list based solution would require constant updates.

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

Answer 1

Are there really that many free webmail providers out there? I would go with a 'blacklisting' style solution.

For example, flag everything in this wikipedia list as free (heck I would think covering gmail/hotmail/yahoo/aol would cover a huge % of users anyway). Then if you get more than 2 (or higher number if your site has high throughput) registrations from the same email domain, it notifies the admin to check the domain to see if it needs to be added to the 'blacklist'.

I would imagine there are much more reliable ways to detect business customers though. For example in Australia you could just ask for an ABN and then check that it's valid. Are you willing to punish small business who don't have email providing and just use a generic @gmail account?

Answer 2

Here is a link to SpamAssasin's freemail list: http://svn.apache.org/repos/asf/spamassassin/trunk/rules/20_freemail_domains.cf.
I suppose, checking against this list is a good start.