Best practices for email address validation (including the + in gmail addresses)
I know there are a lot of questions on here about email validation and specific RegEx's. I'd like to know what the best practices are for validating emails with respect to having the username+anythingelse@gmail.com trick (details here). My current RegExp for JavaScript validation is as follows, but it doesn't support the extra + in the handle:
/^([a-zA-Z0-9_.-])+@(([a-zA-Z0-9-])+.)+([a-zA-Z0-9]{2,4})+$/
Are there any other services that support the extra + ? Should I allow a + in the address or should I alter the RegEx to only allow it for an email with gmail.com or googlemail.com as the domain? If so, what would be the altered RegEx?
UPDATE: Thanks to everyone for pointing out that + is valid per the spec. I didn't know that and now do for the future. For those of you saying that its bad to even use a RegEx to validate it, my reason is completely based on a creative design I'm building to. Our client's design places a green check or a red X next to the email address input on blur of it. That icon indicates whether or not its a valid email address so I must use some JS to validate it then.
+ is a valid character in an email address. It doesn't matter if the domain isn't gmail.com or googlemail.com
Regexes aren't actually a very good way of validating emails, but if you just want to modify your regex to handle the plus, change it to the following:
/^([a-zA-Z0-9_.-+])+@(([a-zA-Z0-9-])+.)+([a-zA-Z0-9]{2,4})+$/
As an example of how this regex doesn't validate against the spec: The email ..@-.com is valid according to it.
If you need to validate emails via regexp, then read the standard or at least this article.
The standard suggests to use this regexp:
(?:[a-z0-9!#$%&'*+/=?^_`{|}~-]+(?:.[a-z0-9!#$%&'*+/=?^_`{|}~-]+)*|"(?:[x01-x08x0bx0cx0e-x1fx21x23-x5bx5d-x7f]|[x01-x09x0bx0cx0e-x7f])*")@(?:(?:[a-z0-9](?:[a-z0-9-]*[a-z0-9])?.)+[a-z0-9](?:[a-z0-9-]*[a-z0-9])?|[(?:(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?).){3}(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?|[a-z0-9-]*[a-z0-9]:(?:[x01-x08x0bx0cx0e-x1fx21-x5ax53-x7f]|[x01-x09x0bx0cx0e-x7f])+)])
If that doesn't scare you, it should :)
I would tend to go with something along the lines of /.+@.+..+/ to check for simple mistakes. Then I would send an email to the address to verify that it actually exists, since most typos will still result in syntactically valid email addresses.
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