E-mail signatures aren’t just for your contact details, they’re also a perfect place to put a note about the app. Add a link to the app here and your tenants will notice it every time you exchange messages.
To change your signature in Microsoft Outlook, open a new message and click the Signature button. Then select “Signatures...” where you’ll find lots of ways to customize your signature and improve it by adding links or images.
If you use Gmail, simply click the cogwheel and then select Settings. You’ll then be able to customize your signature under “Signature” as well.