[kfury]

Oh the edge cases will be so angry. There are a very few engineers at Google who have Gmail account names shorter than 6 characters. It's not the norm, but they exist. Their addresses can't be validated.

I'm sure there are special cases all over the place. It would be nice if Mailgun differentiated between 'this address is just malformed' and 'from what I know of [ISP], this address oughtn't exist'.

[alexk]

Well, you are not forced to reject the email, you can just stick to the unobtrusive spellchecker, that just suggests in case if something suspicious. So the end decision is up to your app.

[kfury]

The spellchecker doesn't actually kick in all that often. The better solution is to give flags back differentiating between 'unlikely' and 'impossible' email addresses.

[blantonl]

I concur. You've got to wonder whether or not the trade off between denying the edge-cases outweighs the benefits of "better" validation.