Validating an email address
But if your address works then why does it matter if it's invalid?
That brings us onto the most important principle in distributed software.
We're launching this as a free service that anyone collecting email through web forms can (and should! You'll need a Mailgun account to use the service, but you don't have to send your emails through Mailgun.
There are acknowledged standards for what constitutes a valid email address.
We take this to mean that all messages you send out should conform carefully to the accepted standards.
Messages you receive should be interpreted as the sender intended so long as the meaning is clear. Getting it right is hard because the RFCs that define the conventions are trying to serve many masters and they document conventions that grew up in the early wild west days of email. There's free code out there in many languages that will do this better than anybody's first attempt. If you do try to write validation code yourself then you should at least test it.
I'm not sure about 5.3.4 final, but it is written that some 5.3.4-snapshot versions also were affected.
regular expression pattern to separate the domain name from the email address.