1) In your Workflow project, go to the 'Publishing' tab and in the section called 'Workflow Type', check the "Auto Start" option.
2) In the 'Auto Start Settings' section, define a 'Schedule'. I set it to an "Every Day Pattern" and then edit that and set the 'Time Pattern' to "Interval" and set that to "00:05:00". This will check the inbox every 5 minutes. Adjust as necessary.
3) Inside the Workflow project workspace, delete the default 'Start' component and search for an 'Auto Start from Email' component and drag it into your project in place of the normal 'Start' component. See image below for example:
4) Edit the 'Auto Start from Email' component and on the 'Setup' tab, plug in your settings for connecting to the email inbox, similar to the following image:
5) Then go to the 'Output' tab to setup the email body type to get and set your Output variable name like the following example shows:
6) Downstream of the 'Auto Start from Email' component, you will now be able to see the output variable and its properties, like the following image shows. Use that to setup how your Send Email component will be formatted with the variable properties you desire.