On 04/22/2026 2:18 AM MDT Marc via dovecot <dovecot@dovecot.org> wrote:

How are messages deleted from large mbox files, are these files completely rewritten? I can't really believe that as some are bigger than the free disk space available.

The mbox is partially rewritten (whenever it is eventually sync'd; see, e.g., mbox_lazy_writes setting).

All messages after the earliest deleted message in the file are re-written and shifted "backwards" to fill the freed space.

There's a reason there is a giant red box at the top of https://doc.dovecot.org/2.4.3/core/config/mailbox_formats/mbox.html

michael