Generating proper 1153 Digests is very important. MIME "Digests" are not true digests in the original sense of providing a readable daily omnibus of list traffic, they are a hack concocted by people who were thrilled with MIME and thought digests were just another way of concatenating messages and files. They don't save much space and they don't provide the same service; most modern mailers capable of "dealing" with them are equally capable of routing individual messages to folders based on headers, which is arguably the better solution for people who don't care about bandwidth or disk space to begin with.