On Wed, Jul 22, 2020 at 23:25:18 -0500, Derek Martin wrote: > On Fri, Jul 17, 2020 at 08:37:50AM +0200, Sebastian Stein wrote: ... > > When I open a folder, I can mark a mail as new. How does mutt keep track of > > this flag? Is this stored inside mbox file? > > Yes. It's stored in a message header in the individual message. This > fact is unfortunately one of the things that slows mbox down, in cases > when it is slower than maildir (namely updating status, specifically, > in this case). It did not take much thought to imagine that making > status updates faster for mbox only required invariably storing > messages with a fixed-length status header, where status updates could > simply overwrite the existing status field in place. Sadly no one did > that.
Dovecot tries to make this possible by padding the heading with extra spaces. Then if the update is minor enough and there is enough space in the header, the update is performed in-place. There might be other caveats that I don't remember; it's been a long while since I looked at that code. Of course changing the status is not the only operation that may end up rewriting the entire mbox. Jeff.
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