If you want to stop Digest from going into the Gmail Spam Folder then you need to create a filter.
1) Go to Gmail and in the search box click the options button
2) In the from field input digest@usedigest.com and click on Create Filter
3) In the filter settings, select Never send it to Spam. You can also select other options to make sure you never miss a Digest, like Always mark it as important and Star it. Click the Create Filter button and from now on the emails you receive from Digest will flow into the primary inbox and never go to spam.
