Using the data detector API for email validation. Still probably uses regular expression under the covers (NSDataDetector is a NSRegularExpression subclass), but at least uses a system method instead of a hand-coded regex pattern.

gistfile1.m

- (BOOL)isValidEmailAddress:(NSString *)text
{
    NSError *error = NULL;
    NSRange textRange = {0, [text length]};
    NSDataDetector *detector = [NSDataDetector dataDetectorWithTypes:NSTextCheckingTypeLink error:&error];
    if (!detector) {
        NSLog(@"Could not instantiate link detector for email validation: %@", error);
        return NO;
    }

    NSTextCheckingResult *result = [detector firstMatchInString:text options:0 range:textRange];
    if (![result.URL.scheme isEqual:@"mailto"]) {
        // No link was detected, or it wasn't an email address
        return NO;
    }
    if (result.range.location > textRange.location || result.range.length < textRange.length) {
        // The detected email address does't span the entire input text
        return NO;
    }

    return YES;
}

See https://gist.github.com/anonymous/3bea53c05336f931bd1d for tests and results.