As someone who has had to implement DNS MX lookups before I can tell you this library will save you a TON of effort and reading through RFCs. I downloaded the library and it appears to be very well thought out and written. DNS Lookups for SPF are included as well, very cool.
I've never understood why doing DNS lookups on a MX record is not supported directly out of the box. I started to implement one many years ago (back in the days of VS 6.0) and never had time to wrap it up.
I haven't looked into this library, yet, but I'm definitely very interested.
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