This regular expression is adapted from a version at regular-expressions.info and is a complete verification of RFC 2822. Source: http://www.cocoawithlove.com/2009/06/verifying-that-string-is-email-address.html. Dedicate article: https://medium.com/@darthpelo/email-validation-in-swift-3-0-acfebe4d879a

EmailValidator.swift

/// Validate email string
///
/// - parameter email: A String that rappresent an email address
///
/// - returns: A Boolean value indicating whether an email is valid. 
func isValid(_ email: String) -> Bool {
    let emailRegEx = "(?:[a-zA-Z0-9!#$%\\&‘*+/=?\\^_`{|}~-]+(?:\\.[a-zA-Z0-9!#$%\\&'*+/=?\\^_`{|}” +
        “~-]+)*|\“(?:[\\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])+)\\])"
    
    let emailTest = NSPredicate(format:"SELF MATCHES[c] %@", emailRegEx)
    return emailTest.evaluate(with: email)
}

Thanks for the snippet! I don't know if it's because of Github's formatting systema but the double quotes are wrong so if you try to copy & paste the code you get compilation errors. The code corrected:

/// Validate email string
///
/// - parameter email: A String that rappresent an email address
///
/// - returns: A Boolean value indicating whether an email is valid. 
func isValid(_ email: String) -> Bool {
    let emailRegEx = "(?:[a-zA-Z0-9!#$%\\&‘*+/=?\\^_`{|}~-]+(?:\\.[a-zA-Z0-9!#$%\\&'*+/=?\\^_`{|}" +
        "~-]+)*|\"(?:[\\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])+)\\])"
    
    let emailTest = NSPredicate(format:"SELF MATCHES[c] %@", emailRegEx)
    return emailTest.evaluate(with: email)
}

@darthpelo @sendoa Updated to be an extension on String. Also updated documentation and formatting: https://gist.github.com/DanielStormApps/28ac56b5edc38ac7023960909b5f6d84

@sendoa and @DanielStormApps thanks and sorry for the delay! My bad!