[tomwalsham]

The best way to improve email delivery is to understand that email addresses represent humans. Address validation and long-term deliverability is primarily a problem of social engineering, not technical.

Ordinarily I'm in favour of things that can improve data quality with minimal user friction, but in this case while it looks like an attractive solution, it's both dangerous _and_ broken.

It's dangerous because if you repeatedly open empty SMTP sessions with major ISPs (and some neckbeard boxen) to validate addresses, you will rapidly fall onto blacklists. Furthermore existence of an address says nothing of the end user's ownership of that address.

It's broken because of the myriad crazy responses that mailservers return -: 5XX errors for soft-bounces, 4XX errors for permanent failures, deliberately dead primary MX server... The web's email infrastructure is so massively fragmented and quirkily non-RFC-compliant you just cannot rely on technical solutions to these problems except at scale of an ESP (disclaimer: I work at PostageApp.com, a transactional ESP, and we tackle this problem on a large scale)

Finally, it fails my 'Spammer Sniff Test': If you think of a clever trick to improve email delivery/opens/responses etc, it's been thought up 10 years ago by spammers and long since added to blocked behaviours in email protection infrastructure.

Check for '@', and craft your email verification process to incentivize following through. For long term delivery (to bypass the mailinator issue) provide value, pure and simple.