diff --git a/rfcs/inactive_users/user_index.md b/rfcs/inactive_users/user_index.md
new file mode 100644
index 000000000..ea594ea69
--- /dev/null
+++ b/rfcs/inactive_users/user_index.md
@@ -0,0 +1,28 @@
+# Inactive users index
+
+## Overview and motivation
+As other task dependency and to provide additional internal statistics the Service needs additional index
+to track users that didn't pass the activation.
+
+## `inactive-users` index
+It's an Additional Redis Sorted Set which contains the list of IDs of the `inactive` users.
+Each item score is equal to the `timestamp` set on user creation.
+
+To avoid hardcoded SET name new `USERS_INACTIVATED` constant introduced.
+
+## Registration process
+When the user succeeds registration but activation not requested, the new entry added to `inactive-users`.
+
+**NOTE:** Old Redis `expire` setting methods left in their place, to save old service behavior.
+
+## Activation process
+When the user succeeds activation the entry deleted from `inactive-users`.
+
+## Index cleanup
+Temporarily add `inactive-users` index cleanup. The functionality will move into one LUA script
+with `delete inactive users` logic. This will save us from `dlock` based implementations and all operations will execute in `one-shot` avoiding race conditions.
+On `registration` cleanup method executes before user creation.
+
+On `activation` cleanup method executes before any checks performed by `activation` action.
+
+
diff --git a/src/actions/activate.js b/src/actions/activate.js
index 783f13029..460eeb778 100644
--- a/src/actions/activate.js
+++ b/src/actions/activate.js
@@ -5,8 +5,11 @@ const jwt = require('../utils/jwt.js');
 const { getInternalData } = require('../utils/userData');
 const getMetadata = require('../utils/getMetadata');
 const handlePipeline = require('../utils/pipelineError.js');
+const { cleanInactiveUsersIndex } = require('../utils/inactiveUsers');
+
 const {
   USERS_INDEX,
+  USERS_INACTIVATED,
   USERS_DATA,
   USERS_REFERRAL_INDEX,
   USERS_PUBLIC_INDEX,
@@ -126,6 +129,9 @@ function activateAccount(data, metadata) {
     .persist(userKey)
     .sadd(USERS_INDEX, userId);
 
+  /* delete user id from the inactive users index */
+  pipeline.zrem(USERS_INACTIVATED, userId);
+
   if (alias) {
     pipeline.sadd(USERS_PUBLIC_INDEX, userId);
   }
@@ -173,7 +179,7 @@ function hook(userId) {
  * @apiParam (Payload) {String} [audience] - additional metadata will be pushed there from custom hooks
  *
  */
-function activateAction({ params }) {
+async function activateAction({ params }) {
   // TODO: add security logs
   // var remoteip = request.params.remoteip;
   const { token, username } = params;
@@ -191,6 +197,9 @@ function activateAction({ params }) {
     erase: config.token.erase,
   };
 
+  // TODO: REMOVEME: Execute `DeleteInactiveUsers` LUA script
+  await cleanInactiveUsersIndex.call(this);
+
   return Promise
     .bind(context)
     .then(verifyRequest)
diff --git a/src/actions/register.js b/src/actions/register.js
index ba0413630..06cbc9383 100644
--- a/src/actions/register.js
+++ b/src/actions/register.js
@@ -22,10 +22,13 @@ const checkLimits = require('../utils/checkIpLimits');
 const challenge = require('../utils/challenges/challenge');
 const handlePipeline = require('../utils/pipelineError');
 const hashPassword = require('../utils/register/password/hash');
+const { cleanInactiveUsersIndex } = require('../utils/inactiveUsers');
+
 const {
   USERS_REF,
   USERS_INDEX,
   USERS_SSO_TO_ID,
+  USERS_INACTIVATED,
   USERS_DATA,
   USERS_USERNAME_TO_ID,
   USERS_ACTIVE_FLAG,
@@ -172,6 +175,9 @@ async function performRegistration({ service, params }) {
     await verifySSO(service, params);
   }
 
+  // TODO: REMOVEME: Execute `DeleteInactiveUsers` LUA script
+  await cleanInactiveUsersIndex.call(service);
+
   const [creatorAudience] = audience;
   const defaultAudience = last(audience);
   const userId = service.flake.next();
@@ -208,7 +214,11 @@ async function performRegistration({ service, params }) {
   pipeline.hset(USERS_USERNAME_TO_ID, username, userId);
 
   if (activate === false && config.deleteInactiveAccounts >= 0) {
+    /* TODO Remove this line when last task in group merged */
     pipeline.expire(userDataKey, config.deleteInactiveAccounts);
+
+    /* Add user id to the inactive users index */
+    redis.zadd(USERS_INACTIVATED, created, userId);
   }
 
   await pipeline.exec().then(handlePipeline);
diff --git a/src/actions/remove.js b/src/actions/remove.js
index cdad191e2..b13b2625a 100644
--- a/src/actions/remove.js
+++ b/src/actions/remove.js
@@ -9,6 +9,7 @@ const getMetadata = require('../utils/getMetadata');
 const handlePipeline = require('../utils/pipelineError');
 const {
   USERS_INDEX,
+  USERS_INACTIVATED,
   USERS_PUBLIC_INDEX,
   USERS_ALIAS_TO_ID,
   USERS_SSO_TO_ID,
@@ -92,6 +93,9 @@ async function removeUser({ params }) {
   transaction.srem(USERS_PUBLIC_INDEX, userId);
   transaction.srem(USERS_INDEX, userId);
 
+  /* Delete user from the inactive users index, if user not activated */
+  transaction.zrem(USERS_INACTIVATED, userId);
+
   // remove metadata & internal data
   transaction.del(key(userId, USERS_DATA));
   transaction.del(key(userId, USERS_METADATA, audience));
diff --git a/src/constants.js b/src/constants.js
index 525284ecc..0c5867e70 100644
--- a/src/constants.js
+++ b/src/constants.js
@@ -6,6 +6,10 @@ module.exports = exports = {
   USERS_PUBLIC_INDEX: 'users-public',
   USERS_REFERRAL_INDEX: 'users-referral',
   ORGANIZATIONS_INDEX: 'organization-iterator-set',
+
+  /* inactive user ids set */
+  USERS_INACTIVATED: 'users-inactivated',
+
   // id mapping
   USERS_ALIAS_TO_ID: 'users-alias',
   USERS_SSO_TO_ID: 'users-sso-hash',
diff --git a/src/utils/inactiveUsers/index.js b/src/utils/inactiveUsers/index.js
new file mode 100644
index 000000000..6c4bb9e80
--- /dev/null
+++ b/src/utils/inactiveUsers/index.js
@@ -0,0 +1,23 @@
+const {
+  USERS_INACTIVATED,
+} = require('../../constants');
+
+/**
+ * NOTE: Contents of this file will be removed when `DeleteInactiveUsers` feature merged.
+ * To avoid `dlock` based locks, index cleanup and inactive user remove process will be merged into one LUA script.
+ */
+
+/**
+ * Cleans Inactive user index from User IDs that not activated in some period
+ * @returns {Promise<void>}
+ */
+async function cleanInactiveUsersIndex() {
+  const { redis } = this;
+  const { deleteInactiveAccounts } = this.config;
+  const expire = Date.now() - (deleteInactiveAccounts * 1000);
+  await redis.zremrangebyscore(USERS_INACTIVATED, '-inf', expire);
+}
+
+module.exports = {
+  cleanInactiveUsersIndex,
+};