Introduced with Dovecot 1.0a4. The point is to have a high performance mail store combining all the best qualities of other mailbox formats. Some behavior can't be universally accepted as optimal, so dbox allows sysadmin to configure those:
- One mail per file, or multiple mails per file? If multiple,
- How large each file can grow? This is a tradeoff between read and expunge performance.
- How old files do we still append new mails to? Helps with incremental backups.
- How often should changed mail metadata (flags and keywords) be written to dbox files, instead of only in Dovecot's index files? This is a tradeoff between reliability and performance.
dbox format isn't finished yet, so it should only be used for testing purposes.