Now that you mention it, I noticed that gmail is doing this to me as well. Since gmail uses machine learning in combination with user feedback to sort and filter emails, I’d assume that either the volume of messages from
roundup.psfhosted.org passed a certain threshold or enough people marked emails coming from there as spam for some reason.
Explicitly using a rule that prevents anything from
roundup.psfhosted.org from being marked is probably the best way to stop it. As far as I’m aware, there’s not anything we can do to prevent this from happening in the first place though.