What is the simplest regular expression to validate emails to not accept them blindly?

Question

When users create an account on my site I want to make server validation for emails to not accept every input.

I will send a confirmation, in a way to do a handshake validation.

I am looking for something simple, not the best, but not too simple that doesn't validate anything. I don't know where limitation must be, since any regular expression will not do the correct validation because is not possible to do it with regular expressions.

I'm trying to limit the sintax and visual complexity inherent to regular expressions, because in this case any will be correct.

What regexp can I use to do that?

Answer 1

^\S+@\S+\.\S+$

Answer 2

I think any regexp is by nature complex, so as twk suggests in his comment, why limit yourself to something that is not really complex, but yet not really straightforward to understand either. Go for a non-regexp solution, or consider choosing a bit more powerful regexp.

Answer 3

It's possible to write a regular expression that only accept email addresses that follow the standards. However, there are some email addresses out there that doesn't strictly follow the standards, but still work.

Here are some simple regular expressions for basic validation:

Contains a @ character:

@

Contains @ and a period somewhere after it:

@.*?\.

Has at least one character before the @, before the period and after it:

.+@.+\..+

Has only one @, at least one character before the @, before the period and after it:

^[^@]+@[^@]+\.[^@]+$

Answer 4

Take your pick.

Here's the one that complies with RFC 2822 Section 3.4.1 ...

(?:[a-z0-9!#$%&'*+/=?^_`{|}~-]+(?:\.[a-z0-9!#$%&'*+/=?^_`{|}~-]+)*|"(?:[\x01-\x08\x0b\x0c\x0e-\x1f\x21\x23-\x5b\x5d-\x7f]|\\[\x01-\x09\x0b\x0c\x0e-\x7f])*")@(?:(?:[a-z0-9](?:[a-z0-9-]*[a-z0-9])?\.)+[a-z0-9](?:[a-z0-9-]*[a-z0-9])?|\[(?:(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.){3}(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?|[a-z0-9-]*[a-z0-9]:(?:[\x01-\x08\x0b\x0c\x0e-\x1f\x21-\x5a\x53-\x7f]|\\[\x01-\x09\x0b\x0c\x0e-\x7f])+)\])

Just in case you are curious. :)