I think this is because it is not a physical change, i.e., a change that will be reflected in the file if the buffer is saved. To perform a physical change on the file you need to add C-u before the sorting command. In this case, *if there is an actual rearrangement of messages*, the buffer modified marker (*) will appear and when saving the file will be modified. I also got a bit confused by this the first time I ran into it, but it makes a lot if sense. Cheers, --Manuel
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