Special files under dovecot mail box

[hfh at cndns.com]

Hello, even if all the mails(messages) are deleted from my mail box (such as the sent box), the capacity of the following special files will not change, that is, these files will only increase and easily occupy the disk. Is there any other way besides using doveadm index manually? In addition, will these files be affected if they are deleted?

-rw-------. 1 vmail vmail   3912 Dec  1 13:52 dovecot.index
-rw-------. 1 vmail vmail 127008 Dec 17 17:21 dovecot.index.cache
-rw-------. 1 vmail vmail  18800 Dec 17 17:21 dovecot.index.log
-rw-------. 1 vmail vmail   1567 Jun 20  2019 dovecot.index.thread

Dovecot version is 2.2.36.
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