breaking the mail index
Tangentially query: is Dveocot smart enough to optimize mailbox renaming to do index renaming (i.e. does not try to copy or recreate indices)?
Dovecot is, if you use LAYOUT=index. This will use only mailbox GUID on disk, and the folder name is only in indexes (both list index and mailbox index for recovery purposes).
I would recommend using 2.3.21 with LAYOUT=index to avoid problems.
So you can just add this to an existing configuration, without the need to do anything? Like eg reindex or so? I always had the impression this affects how messages are stored.
mail_location = mdbox:xxxxxx:INDEX=xxxxxx:CONTROL=/xxxxxxx becomes: mail_location = mdbox:xxxxxx:INDEX=xxxxxx:CONTROL=/xxxxxxx:LAYOUT:index
Does this really speed things up?
[1] https://doc.dovecot.org/configuration_manual/mail_location/