In Comcast's latest Open-Xchange "Appsuite" webmail ("connect.xfinity.com/appsuite/..."), the delete schedule can't be adjusted. Messages are deleted from the Spam folder after 7 days, and from the Trash folder after 14. The contents of all other folders are retained indefinitely as long as you log in to each of your email IDs at least once every 12 months. See https://www.xfinity.com/support/articles/set-email-deletion-settings and https://www.xfinity.com/support/articles/email-activity.
Thanks for the information. I remember "back in the day" that the user could set parameters for how long, up to a point, that emails could be saved in these folders (at least the trash folder). C"est la vie.