It's been four years and I don't have access to the code or the testset (work for a customer), sorry.It would have been nice to have that bit open sourced though, jvde if you are reading this, hint!The proper way seems to be: do your verification anyway, if the address appears to be invalid prompt the user once more to please check their email address and if they indicate it is ok then simply send the verification email assuming the user knows what they are doing.This will catch a very large chunk of accidentally mis-spelled email addresses and will allow the users to override the validator for strange edge cases.CFWS is legal to insert in the written representation of the email address in RFC 5322 and RFC 5321, but it is not a structural part of the email address (you get the email address by deleting all such instances).* Everything to the right of the @ is either a domain name, an IPv4 address literal embedded in , or an IPv6 address literal prefixed with IPv6: and embedded in  (e.g., [IPv6:::1]).* Enclosing a localpart in quotes does not change the email address.
Considering that the email address might just be misspelled or the user might not exist anyway, it doesn't seem very productive to try to do much validation, other than maybe catch the very obvious invalid cases to cut down on your email sending costs somewhat.I also consider the relative dexterity of the fingers.We all know that the pinky is the retarded cousin of the finger family, so that is factored in as well. And again, those bad keys are only invalid in certain circumstances.We are developers, we are technical folk, so it’s no surprise that the prevailing wisdom is to check that it matches the official criteria, some examples of the diversity of the official criteria are…If you have a well laid-out form with a label that says “email”, and the user enters an ‘@’ symbol somewhere, then it’s safe to say they understood that they were supposed to be entering an email address. Next, we want to do some validation to ascertain if they correctly entered right?