Is there a standard way to generate a QR code and attach it to a mail item from iOS client app (no server code)?
Since iOS 7, you can use a Core Image filter to generate QR images. See the final tip here:
- (CIImage *)createQRForString:(NSString *)qrString {
NSData *stringData = [qrString dataUsingEncoding: NSISOLatin1StringEncoding];
CIFilter *qrFilter = [CIFilter filterWithName:@"CIQRCodeGenerator"];
[qrFilter setValue:stringData forKey:@"inputMessage"];
return qrFilter.outputImage;
}