[fsckin]

I was hoping that this did something a bit more worthy of Hacker News, like checking if the A Record exists. Or perhaps speaking SMTP to the domain in question to query if the user actually exists (works on some domains) using web sockets.

http://www.webdigi.co.uk/blog/2009/how-to-check-if-an-email-...

Maybe I'll build it for fun.

[bryanh]

I started on this once upon a time: http://emailpie.com/

Might be fun to do the same in JS.

[eli]

The only way to check an address is to send it an email. Hotmial.com has valid DNS, for example.

[idle_processor]

Why use the A record, rather than MX?

[petercooper]

Strictly, you might need to check for both. If there are no MX records, mail will be delivered to the @ A record for a domain (e.g. mail to [e-mail] will go to the IP for 'example.com').

So if there are no MX records, you need to check @'s A record as well (or vice versa, since not all domains have A records either).

[MichaelApproved]

MX server record isn't required for all DNS listed email domains.