[twakefield]

Great work and thanks for the mention. We've been thinking about doing something similar but going a little further and actually checking mx records, with a response if they don't exist. This would help with the long tail domains.

Edit: Another good idea from hinathan.

[eli]

Be careful. Some legit domains might not have an MX record. (but could still work; messages will usually go to the A address)

[dko]

No problem! The Mailgun webhooks helped us collect and analyze the delivery failures, so that was really helpful. Thanks for that.

A mx checking service sounds awesome. Keep us posted if you guys do it.

[asuth]

Just doing DNS checks might not be enough:

`$ dig hotnail.com MX` yields results but is still invalid.

[Zarel]

Well, technically, it's valid; it's just unlikely to be what you meant to type. That sort of case should probably be handled separately.

[jtheory]

Well worth noting: auto-correcting the email addresses would be a very bad idea; ditto for stopping them from submitting the form if this is triggered.

But just showing a little note "are you sure you didn't mean [e-mail]", then letting them submit anyway, isn't generally annoying even for misfires.

Because there actually are going to be occasional users who mistype "ymail.com" when they mean gmail. Hey, thanks for the warning; the y is right near the g.