Suppose I want to move all message from a specific host to another folder. UPDATE table SET folder=new-folder WHERE host=value;

With databases you can do things you would have to write complex

Marc Perkel: programs

to do with files. Things that you would consider to be impossible are trivial with databases.

This outside the box.

People who optimise their systems for shiny cute features rather than the common case get all the hacks they deserve.

Repeat after me: design for the common case.

Also your proposed sql above and implications (arbitrary operations based on mail metadata i.e. headers) seems to involve indexing every mail header on delivery. Good luck with that one large scale mail storage. Did you want a mail database, or an OLAP system? >-)

/jg