diff --git a/CHANGELOG.md b/CHANGELOG.md
index 65324fb6..13dc2a49 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -2,6 +2,8 @@
 
 ## untagged
 
+- dovecot: keep mailbox index only in memory to avoid unnecessary disc usage 
+  ([#632](https://github.com/chatmail/relay/pull/632))
 
 ## 1.7.0 2025-09-11
 
diff --git a/cmdeploy/src/cmdeploy/dovecot/dovecot.conf.j2 b/cmdeploy/src/cmdeploy/dovecot/dovecot.conf.j2
index f6511be0..244a58e6 100644
--- a/cmdeploy/src/cmdeploy/dovecot/dovecot.conf.j2
+++ b/cmdeploy/src/cmdeploy/dovecot/dovecot.conf.j2
@@ -68,7 +68,7 @@ userdb {
 ##
 
 # Mailboxes are stored in the "mail" directory of the vmail user home.
-mail_location = maildir:{{ config.mailboxes_dir }}/%u
+mail_location = maildir:{{ config.mailboxes_dir }}/%u:INDEX=MEMORY
 
 namespace inbox {
   inbox = yes