spam emails being generated from Nextdoor application

When I send or receive a personal message within the Nextdoor application, I get a spam email to my comcast.net email address (which is my Nextdoor contact email address). The spam email shows as "Delivery to the following recipients was aborted after [n.n] hour(s): * spam@uce.gov.

Nextdoor is trying to send me an email alerting me to a message in their application, but Xfinity (Comcast) is apparently treating it as spam and creating an email to uce.gov? Is there a filter setting or some other setting that can prevent this?