Proper Email Regular Expresssion Validation in c# [duplicate]

Question

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How can I validate an email address using a regular expression? (73 answers)

Closed 9 years ago.

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As far as I found more than 20 Email validation regular expressions But all of them allows

a@a.co.in.in.in.in.in.in.in

as valid email address!!!

I want to restrict that only two dots(.) should be allowed.

For Example:

Valid Emails

somename@yahoo.in

somename@yahoo.co.in

somename@somesite.bizz

somename@gmail.com

somename@somesite.net

Invalid Emails

@.co

@a.com

a@a

a@.com

a@a.co.in.in //maximum two dots allowed otherwise invalid

a@a.co.in.in.in.in.in.in //maximum two dots allowed otherwise invalid

For this I tried with

[a-zA-Z0-9._%+-]+@[a-zA-Z0-9]+\.[a-zA-Z]{2,5}[\.[a-zA-Z]{2,5}]{0,1}

It is working with 2 dots but throwing invalid message for

somename@somesite.com

Answer 1

I think that it should be like

[a-zA-Z0-9._%+-]+@[a-zA-Z0-9]+\.[a-zA-Z]{2,5}(\.[a-zA-Z]{2,5}){0,1}

I'm not experienced in regex, but I think that [.[a-zA-Z]{2,5}] is considered character group. Parentheses do the trick.

Answer 2

One possible approach is to first validate with one of the existing regular expressions that allows the email address a@a.co.in.in.in.in.in.in.in. If it validates, then do the following steps.

1. Do a String split on the @ sign.
2. Take the right hand side of the split, and do a split on the period .
3. If the resulting array has length 2 or 3, then you have found a domain that satisfies your definition of a valid email. If not, then reject.

This way, you let regex you already found handle the grunt work, and you just check for the one additional condition you care about.