There are 3 steps to get UDID of a device with iOS.
- Connect device to the computer.
- Run iTunes
- Copy UDID from information screen.
Connect your device (iPhone, iPad, iPod) to the computer with USB cable. Run
iTunes. iTunes can also start automatically. If you do not have iTunes,
download it from the producer's web page.
After connecting the device and running iTunes, you will see screen like this:

Click on icon on the top left corner. A sum-up screen will be shown:

Click the serial number. Number will change to UDID:

Right-click on UDID and from the pop-up menu confirm left-clicking copying UDID number. Done! Now you can send it via email.