F. H. Muffman said:
Not every solution will work for every person.
If you need it to be dynamic (which I didn't get any indication that the
original person needed dynamicosity), then you'd need to build a DLL that
can be used as a custom action on a rule to pull out the senders domain and
then drop it in an unused field (like Mileage) and group by that.
Personally, I'd work through my email one by one and build a search folder
as needed. I hit message 1, it's from somedomain.what, I build a search
folder. Take care of all the messages. I go back, hit what should now be
message 1, it's from otherdomain.what, I edit the search folder, I take care
of all the messages.