You would like to send a QR code to your contacts so that you can use the QR code scanner of the check-in app?
Open the message in which you want to send the QR code and then open the placeholder manager. Now click on "Contact Information" and select the placeholder "QR Code" at the bottom.
This is what your e-mail will look like:
And the contact receives the following view after sending:
Towards a greener world
You can actively inform the participants in the e-mail that the QR code does not have to be printed out. The QR code can be scanned directly from the contact's smartphone.