diff --git a/src/imap/imap-client.c b/src/imap/imap-client.c
index 4931160350..9404b8c426 100644
--- a/src/imap/imap-client.c
+++ b/src/imap/imap-client.c
@@ -24,6 +24,7 @@
 #include "imap-search.h"
 #include "imap-notify.h"
 #include "imap-commands.h"
+#include "imap-feature.h"
 
 #include <unistd.h>
 
@@ -39,8 +40,8 @@ struct imap_module_register imap_module_register = { 0 };
 struct client *imap_clients = NULL;
 unsigned int imap_client_count = 0;
 
-unsigned int imap_feature_condstore = MAILBOX_FEATURE_CONDSTORE;
-unsigned int imap_feature_qresync = MAILBOX_FEATURE_QRESYNC;
+unsigned int imap_feature_condstore = UINT_MAX;
+unsigned int imap_feature_qresync = UINT_MAX;
 
 static const char *client_command_state_names[CLIENT_COMMAND_STATE_DONE+1] = {
 	"wait-input",
@@ -153,6 +154,7 @@ struct client *client_create(int fd_in, int fd_out, const char *session_id,
 	client->user = user;
 	client->notify_count_changes = TRUE;
 	client->notify_flag_changes = TRUE;
+	p_array_init(&client->enabled_features, client->pool, 8);
 
 	if (set->rawlog_dir[0] != '\0') {
 		(void)iostream_rawlog_create(set->rawlog_dir, &client->input,
@@ -1449,24 +1451,39 @@ bool client_handle_search_save_ambiguity(struct client_command_context *cmd)
 
 void client_enable(struct client *client, unsigned int feature_idx)
 {
-	enum mailbox_feature features = feature_idx;
+	if (client_has_enabled(client, feature_idx))
+		return;
+
+	const struct imap_feature *feat = imap_feature_idx(feature_idx);
+	feat->callback(client);
+	/* set after the callback, so the callback can see what features were
+	   previously set */
+	bool value = TRUE;
+	array_idx_set(&client->enabled_features, feature_idx, &value);
+}
+
+bool client_has_enabled(struct client *client, unsigned int feature_idx)
+{
+	if (feature_idx >= array_count(&client->enabled_features))
+		return FALSE;
+	const bool *featurep =
+		array_idx(&client->enabled_features, feature_idx);
+	return *featurep;
+}
+
+static void imap_client_enable_condstore(struct client *client)
+{
 	struct mailbox_status status;
-	bool had_condstore = client_has_enabled(client, imap_feature_condstore);
 	int ret;
 
-	if ((features & imap_feature_qresync) != 0)
-		features |= imap_feature_condstore;
-
-	if ((client->enabled_features & features) == features)
+	if (client->mailbox == NULL)
 		return;
 
-	client->enabled_features |= features;
-	if (client->mailbox == NULL)
+	if ((client_enabled_mailbox_features(client) & MAILBOX_FEATURE_CONDSTORE) != 0)
 		return;
 
-	ret = mailbox_enable(client->mailbox, features);
-	if (ret == 0 && !had_condstore &&
-	    client_has_enabled(client, imap_feature_condstore)) {
+	ret = mailbox_enable(client->mailbox, MAILBOX_FEATURE_CONDSTORE);
+	if (ret == 0) {
 		/* CONDSTORE being enabled while mailbox is selected.
 		   Notify client of the latest HIGHESTMODSEQ. */
 		ret = mailbox_get_status(client->mailbox,
@@ -1483,31 +1500,46 @@ void client_enable(struct client *client, unsigned int feature_idx)
 	}
 }
 
-bool client_has_enabled(struct client *client, unsigned int feature_idx)
+static void imap_client_enable_qresync(struct client *client)
 {
-	enum mailbox_feature features = feature_idx;
-
-	return (client->enabled_features & features) != 0;
+	/* enable also CONDSTORE */
+	client_enable(client, imap_feature_condstore);
 }
 
 enum mailbox_feature client_enabled_mailbox_features(struct client *client)
 {
-	return client->enabled_features;
+	enum mailbox_feature mailbox_features = 0;
+	const struct imap_feature *feature;
+	const bool *client_enabled;
+	unsigned int count;
+
+	client_enabled = array_get(&client->enabled_features, &count);
+	for (unsigned int idx = 0; idx < count; idx++) {
+		if (client_enabled[idx]) {
+			feature = imap_feature_idx(idx);
+			mailbox_features |= feature->mailbox_features;
+		}
+	}
+	return mailbox_features;
 }
 
 const char *const *client_enabled_features(struct client *client)
 {
-	static const char *condstore_str = "CONDSTORE";
-	static const char *qresync_str = "QRESYNC";
-	ARRAY_TYPE(const_string) features;
-	t_array_init(&features, 8);
-
-	if ((client->enabled_features & imap_feature_condstore) != 0)
-		array_append(&features, &condstore_str, 1);
-	if ((client->enabled_features & imap_feature_qresync) != 0)
-		array_append(&features, &qresync_str, 1);
-	array_append_zero(&features);
-	return array_idx(&features, 0);
+	ARRAY_TYPE(const_string) feature_strings;
+	const struct imap_feature *feature;
+	const bool *client_enabled;
+	unsigned int count;
+
+	t_array_init(&feature_strings, 8);
+	client_enabled = array_get(&client->enabled_features, &count);
+	for (unsigned int idx = 0; idx < count; idx++) {
+		if (client_enabled[idx]) {
+			feature = imap_feature_idx(idx);
+			array_append(&feature_strings, &feature->feature, 1);
+		}
+	}
+	array_append_zero(&feature_strings);
+	return array_idx(&feature_strings, 0);
 }
 
 struct imap_search_update *
@@ -1542,6 +1574,17 @@ void client_search_updates_free(struct client *client)
 	array_clear(&client->search_updates);
 }
 
+void clients_init(void)
+{
+	imap_feature_condstore =
+		imap_feature_register("CONDSTORE", MAILBOX_FEATURE_CONDSTORE,
+				      imap_client_enable_condstore);
+	imap_feature_qresync =
+		imap_feature_register("QRESYNC", MAILBOX_FEATURE_QRESYNC |
+				      MAILBOX_FEATURE_CONDSTORE,
+				      imap_client_enable_qresync);
+}
+
 void clients_destroy_all(void)
 {
 	while (imap_clients != NULL) {
diff --git a/src/imap/imap-client.h b/src/imap/imap-client.h
index d391587029..11e541730c 100644
--- a/src/imap/imap-client.h
+++ b/src/imap/imap-client.h
@@ -166,7 +166,7 @@ struct client {
         struct mailbox_keywords keywords;
 	unsigned int sync_counter;
 	uint32_t messages_count, recent_count, uidvalidity;
-	enum mailbox_feature enabled_features;
+	ARRAY(bool) enabled_features;
 
 	time_t last_input, last_output;
 	unsigned int bad_counter;
@@ -338,6 +338,7 @@ void client_input(struct client *client);
 bool client_handle_input(struct client *client);
 int client_output(struct client *client);
 
+void clients_init(void);
 void clients_destroy_all(void);
 
 #endif
diff --git a/src/imap/imap-feature.c b/src/imap/imap-feature.c
index fe556a672f..d8d52b8c7e 100644
--- a/src/imap/imap-feature.c
+++ b/src/imap/imap-feature.c
@@ -3,13 +3,44 @@
 #include "imap-common.h"
 #include "imap-feature.h"
 
+static ARRAY_TYPE(imap_feature) feature_register = ARRAY_INIT;
+
 bool imap_feature_lookup(const char *name, unsigned int *feature_idx_r)
 {
-	if (strcasecmp(name, "CONDSTORE") == 0)
-		*feature_idx_r = imap_feature_condstore;
-	else if (strcasecmp(name, "QRESYNC") == 0)
-		*feature_idx_r = imap_feature_qresync;
-	else
-		return FALSE;
-	return TRUE;
+	for (unsigned int idx = 0; idx < array_count(&feature_register); idx++) {
+		const struct imap_feature *feat =
+			array_idx(&feature_register, idx);
+		if (strcasecmp(name, feat->feature) == 0) {
+			*feature_idx_r = idx;
+			return TRUE;
+		}
+	}
+	return FALSE;
+}
+
+const struct imap_feature *imap_feature_idx(unsigned int feature_idx)
+{
+	return array_idx(&feature_register, feature_idx);
+}
+
+unsigned int
+imap_feature_register(const char *feature, enum mailbox_feature mailbox_features,
+		      imap_client_enable_callback_t *callback)
+{
+	struct imap_feature *feat = array_append_space(&feature_register);
+	feat->feature = feature;
+	feat->mailbox_features = mailbox_features;
+	feat->callback = callback;
+	return array_count(&feature_register)-1;
+}
+
+void imap_features_init(void)
+{
+	i_assert(!array_is_created(&feature_register));
+	i_array_init(&feature_register, 8);
+}
+
+void imap_features_deinit(void)
+{
+	array_free(&feature_register);
 }
diff --git a/src/imap/imap-feature.h b/src/imap/imap-feature.h
index 7b0742a24f..a96aa6e4c5 100644
--- a/src/imap/imap-feature.h
+++ b/src/imap/imap-feature.h
@@ -1,6 +1,24 @@
 #ifndef IMAP_FEATURE_H
 #define IMAP_FEATURE_H
 
+typedef void imap_client_enable_callback_t(struct client *);
+
+struct imap_feature {
+	const char *feature;
+	enum mailbox_feature mailbox_features;
+	imap_client_enable_callback_t *callback;
+	bool enabled;
+};
+ARRAY_DEFINE_TYPE(imap_feature, struct imap_feature);
+
 bool imap_feature_lookup(const char *name, unsigned int *feature_idx_r);
+const struct imap_feature *imap_feature_idx(unsigned int feature_idx);
+
+unsigned int
+imap_feature_register(const char *feature, enum mailbox_feature mailbox_features,
+		      imap_client_enable_callback_t *callback);
+
+void imap_features_init(void);
+void imap_features_deinit(void);
 
 #endif
diff --git a/src/imap/main.c b/src/imap/main.c
index b275ae9c89..6b43de1ce9 100644
--- a/src/imap/main.c
+++ b/src/imap/main.c
@@ -21,6 +21,7 @@
 #include "imap-master-client.h"
 #include "imap-resp-code.h"
 #include "imap-commands.h"
+#include "imap-feature.h"
 #include "imap-fetch.h"
 
 #include <stdio.h>
@@ -481,6 +482,8 @@ int main(int argc, char *argv[])
 	/* plugins may want to add commands, so this needs to be called early */
 	commands_init();
 	imap_fetch_handlers_init();
+	imap_features_init();
+	clients_init();
 	imap_master_clients_init();
 
 	const char *error;
@@ -525,6 +528,8 @@ int main(int argc, char *argv[])
 	mail_storage_service_deinit(&storage_service);
 
 	imap_fetch_handlers_deinit();
+	imap_features_deinit();
+
 	commands_deinit();
 	imap_master_clients_deinit();