Complexities of e-mail validation logic
If your email is <RFC>fan 69™@root I am not going to let you signup. Sending emails cost money and bouncing emails affects your sender reputation. Also, for every user out there using <RFC>fan 69™@root as their email address, there is going to be thousands of people accidently entering their email address incorrectly and not getting a alert about it. Yes you could do fancy shit like checking mx records and whatnot, but come on- Im not going to maintain/build that infrastructure for the one out of a million people who are trying to use that address.<p>Developer time is precious at a startup and supporting <RFC>fan 69™@root while still denying b ob@gmailcom is very, very far down the list of things to do.<p>In summary: I don't suggest doing 'perfect' email validation to RFC spec. You will save money/devtime and make more of your users happy by not doing it.