diff --git a/chatmaild/src/chatmaild/config.py b/chatmaild/src/chatmaild/config.py
index 38c955c8..38272244 100644
--- a/chatmaild/src/chatmaild/config.py
+++ b/chatmaild/src/chatmaild/config.py
@@ -56,6 +56,7 @@ class Config:
         self.privacy_mail = params.get("privacy_mail")
         self.privacy_pdo = params.get("privacy_pdo")
         self.privacy_supervisor = params.get("privacy_supervisor")
+        self.tmpfs_index = params.get("tmpfs_index", "false").lower() == "true"
 
         # deprecated option
         mbdir = params.get("mailboxes_dir", f"/home/vmail/mail/{self.mail_domain}")
diff --git a/chatmaild/src/chatmaild/ini/chatmail.ini.f b/chatmaild/src/chatmaild/ini/chatmail.ini.f
index 29d7baa9..a5236234 100644
--- a/chatmaild/src/chatmaild/ini/chatmail.ini.f
+++ b/chatmaild/src/chatmaild/ini/chatmail.ini.f
@@ -48,6 +48,9 @@ passthrough_senders =
 # (space-separated, item may start with "@" to whitelist whole recipient domains)
 passthrough_recipients =
 
+# store index files in tmpfs (good for disk size and I/O, bad for ram)
+tmpfs_index = false
+
 # path to www directory - documented here: https://chatmail.at/doc/relay/getting_started.html#custom-web-pages
 #www_folder = www
 
diff --git a/chatmaild/src/chatmaild/ini/override-testrun.ini b/chatmaild/src/chatmaild/ini/override-testrun.ini
index af337173..ff3738d0 100644
--- a/chatmaild/src/chatmaild/ini/override-testrun.ini
+++ b/chatmaild/src/chatmaild/ini/override-testrun.ini
@@ -1,3 +1,6 @@
+[params]
+
+tmpfs_index = true
 
 [privacy]
 
diff --git a/cmdeploy/src/cmdeploy/dovecot/dovecot.conf.j2 b/cmdeploy/src/cmdeploy/dovecot/dovecot.conf.j2
index 8ab2de56..bc15766d 100644
--- a/cmdeploy/src/cmdeploy/dovecot/dovecot.conf.j2
+++ b/cmdeploy/src/cmdeploy/dovecot/dovecot.conf.j2
@@ -68,7 +68,11 @@ userdb {
 ##
 
 # Mailboxes are stored in the "mail" directory of the vmail user home.
+{% if config.tmpfs_index %}
+mail_location = maildir:{{ config.mailboxes_dir }}/%u:INDEX=/dev/shm/%u
+{% else %}
 mail_location = maildir:{{ config.mailboxes_dir }}/%u
+{% endif %}
 
 # index/cache files are not very useful for chatmail relay operations 
 # but it's not clear how to disable them completely.