distribution groups using Outlook 2010/2013 - Unable to modify or add users
I am absolutely having this same issue, and have been for a couple months now. I have old, existing distribution lists that work fine but I cannot edit, and I can't create new lists or change members.
An interesting thing I have noticed is that when I create lists now it gives them an "Alias name" that is a number now instead of the underscored (list_name_domain_com) style. Also, it lists the user who created the list as the "owner" instead of leaving that field blank like it did on previous distribution lists.
My concern is that this is actually an issue with the way that Comcast's software is creating the list itself, and not that there is something inherently wrong with Exchange as most Comcast reps have been indicating. This is sort of insane, because this is the sort of thing I would expect from a small-time local ISP or something, but at least in that case they'd have someone fix it.