diff --git a/CHANGES.md b/CHANGES.md
index 4a6133c103..c2c287eb20 100644
--- a/CHANGES.md
+++ b/CHANGES.md
@@ -6,6 +6,7 @@ Features ✨:
 
 Improvements 🙌:
  - Open an existing DM instead of creating a new one (#2319)
+ - Ask for explicit user consent to send their contact details to the identity server (#2375)
 
 Bugfix 🐛:
  - Fix issue when restoring draft after sharing (#2287)
diff --git a/vector/src/main/java/im/vector/app/features/contactsbook/ContactsBookAction.kt b/vector/src/main/java/im/vector/app/features/contactsbook/ContactsBookAction.kt
index 8eb5bc733b..e380998fd2 100644
--- a/vector/src/main/java/im/vector/app/features/contactsbook/ContactsBookAction.kt
+++ b/vector/src/main/java/im/vector/app/features/contactsbook/ContactsBookAction.kt
@@ -21,4 +21,5 @@ import im.vector.app.core.platform.VectorViewModelAction
 sealed class ContactsBookAction : VectorViewModelAction {
     data class FilterWith(val filter: String) : ContactsBookAction()
     data class OnlyBoundContacts(val onlyBoundContacts: Boolean) : ContactsBookAction()
+    object UserConsentGranted : ContactsBookAction()
 }
diff --git a/vector/src/main/java/im/vector/app/features/contactsbook/ContactsBookFragment.kt b/vector/src/main/java/im/vector/app/features/contactsbook/ContactsBookFragment.kt
index c4cf9eab39..23d21f5240 100644
--- a/vector/src/main/java/im/vector/app/features/contactsbook/ContactsBookFragment.kt
+++ b/vector/src/main/java/im/vector/app/features/contactsbook/ContactsBookFragment.kt
@@ -18,6 +18,7 @@ package im.vector.app.features.contactsbook
 
 import android.os.Bundle
 import android.view.View
+import androidx.appcompat.app.AlertDialog
 import androidx.core.view.isVisible
 import com.airbnb.mvrx.activityViewModel
 import com.airbnb.mvrx.withState
@@ -57,10 +58,26 @@ class ContactsBookFragment @Inject constructor(
         sharedActionViewModel = activityViewModelProvider.get(UserDirectorySharedActionViewModel::class.java)
         setupRecyclerView()
         setupFilterView()
+        setupConsentView()
         setupOnlyBoundContactsView()
         setupCloseView()
     }
 
+    private fun setupConsentView() {
+        phoneBookSearchForMatrixContacts.setOnClickListener {
+            withState(contactsBookViewModel) { state ->
+                AlertDialog.Builder(requireActivity())
+                        .setTitle(R.string.identity_server_consent_dialog_title)
+                        .setMessage(getString(R.string.identity_server_consent_dialog_content, state.identityServerUrl ?: ""))
+                        .setPositiveButton(R.string.yes) { _, _ ->
+                            contactsBookViewModel.handle(ContactsBookAction.UserConsentGranted)
+                        }
+                        .setNegativeButton(R.string.no, null)
+                        .show()
+            }
+        }
+    }
+
     private fun setupOnlyBoundContactsView() {
         phoneBookOnlyBoundContacts.checkedChanges()
                 .subscribe {
@@ -98,6 +115,7 @@ class ContactsBookFragment @Inject constructor(
     }
 
     override fun invalidate() = withState(contactsBookViewModel) { state ->
+        phoneBookSearchForMatrixContacts.isVisible = state.filteredMappedContacts.isNotEmpty() && state.identityServerUrl != null && !state.userConsent
         phoneBookOnlyBoundContacts.isVisible = state.isBoundRetrieved
         contactsBookController.setData(state)
     }
diff --git a/vector/src/main/java/im/vector/app/features/contactsbook/ContactsBookViewModel.kt b/vector/src/main/java/im/vector/app/features/contactsbook/ContactsBookViewModel.kt
index 167660d11e..2c4c5d0596 100644
--- a/vector/src/main/java/im/vector/app/features/contactsbook/ContactsBookViewModel.kt
+++ b/vector/src/main/java/im/vector/app/features/contactsbook/ContactsBookViewModel.kt
@@ -38,11 +38,10 @@ import kotlinx.coroutines.launch
 import org.matrix.android.sdk.api.MatrixCallback
 import org.matrix.android.sdk.api.session.Session
 import org.matrix.android.sdk.api.session.identity.FoundThreePid
+import org.matrix.android.sdk.api.session.identity.IdentityServiceError
 import org.matrix.android.sdk.api.session.identity.ThreePid
 import timber.log.Timber
 
-private typealias PhoneBookSearch = String
-
 class ContactsBookViewModel @AssistedInject constructor(@Assisted
                                                         initialState: ContactsBookViewState,
                                                         private val contactsDataSource: ContactsDataSource,
@@ -85,7 +84,9 @@ class ContactsBookViewModel @AssistedInject constructor(@Assisted
     private fun loadContacts() {
         setState {
             copy(
-                    mappedContacts = Loading()
+                    mappedContacts = Loading(),
+                    identityServerUrl = session.identityService().getCurrentIdentityServerUrl(),
+                    userConsent = session.identityService().getUserConsent()
             )
         }
 
@@ -109,6 +110,9 @@ class ContactsBookViewModel @AssistedInject constructor(@Assisted
     }
 
     private fun performLookup(data: List<MappedContact>) {
+        if (!session.identityService().getUserConsent()) {
+            return
+        }
         viewModelScope.launch {
             val threePids = data.flatMap { contact ->
                 contact.emails.map { ThreePid.Email(it.email) } +
@@ -116,8 +120,14 @@ class ContactsBookViewModel @AssistedInject constructor(@Assisted
             }
             session.identityService().lookUp(threePids, object : MatrixCallback<List<FoundThreePid>> {
                 override fun onFailure(failure: Throwable) {
-                    // Ignore
                     Timber.w(failure, "Unable to perform the lookup")
+
+                    // Should not happen, but just to be sure
+                    if (failure is IdentityServiceError.UserConsentNotProvided) {
+                        setState {
+                            copy(userConsent = false)
+                        }
+                    }
                 }
 
                 override fun onSuccess(data: List<FoundThreePid>) {
@@ -171,9 +181,21 @@ class ContactsBookViewModel @AssistedInject constructor(@Assisted
         when (action) {
             is ContactsBookAction.FilterWith        -> handleFilterWith(action)
             is ContactsBookAction.OnlyBoundContacts -> handleOnlyBoundContacts(action)
+            ContactsBookAction.UserConsentGranted   -> handleUserConsentGranted()
         }.exhaustive
     }
 
+    private fun handleUserConsentGranted() {
+        session.identityService().setUserConsent(true)
+
+        setState {
+            copy(userConsent = true)
+        }
+
+        // Perform the lookup
+        performLookup(allContacts)
+    }
+
     private fun handleOnlyBoundContacts(action: ContactsBookAction.OnlyBoundContacts) {
         setState {
             copy(
diff --git a/vector/src/main/java/im/vector/app/features/contactsbook/ContactsBookViewState.kt b/vector/src/main/java/im/vector/app/features/contactsbook/ContactsBookViewState.kt
index 3e4f4ddcb6..d2ee684c4d 100644
--- a/vector/src/main/java/im/vector/app/features/contactsbook/ContactsBookViewState.kt
+++ b/vector/src/main/java/im/vector/app/features/contactsbook/ContactsBookViewState.kt
@@ -26,10 +26,14 @@ data class ContactsBookViewState(
         val mappedContacts: Async<List<MappedContact>> = Loading(),
         // Use to filter contacts by display name
         val searchTerm: String = "",
-        // Tru to display only bound contacts with their bound 2pid
+        // True to display only bound contacts with their bound 2pid
         val onlyBoundContacts: Boolean = false,
         // All contacts, filtered by searchTerm and onlyBoundContacts
         val filteredMappedContacts: List<MappedContact> = emptyList(),
         // True when the identity service has return some data
-        val isBoundRetrieved: Boolean = false
+        val isBoundRetrieved: Boolean = false,
+        // The current identity server url if any
+        val identityServerUrl: String? = null,
+        // User consent to perform lookup (send emails to the identity server)
+        val userConsent: Boolean = false
 ) : MvRxState
diff --git a/vector/src/main/res/layout/fragment_contacts_book.xml b/vector/src/main/res/layout/fragment_contacts_book.xml
index eb90da1bbe..1f8566e05e 100644
--- a/vector/src/main/res/layout/fragment_contacts_book.xml
+++ b/vector/src/main/res/layout/fragment_contacts_book.xml
@@ -93,6 +93,27 @@
             app:layout_constraintTop_toBottomOf="@+id/phoneBookFilterContainer"
             tools:visibility="visible" />
 
+        <com.google.android.material.button.MaterialButton
+            android:id="@+id/phoneBookSearchForMatrixContacts"
+            style="@style/VectorButtonStyleText"
+            android:layout_width="wrap_content"
+            android:layout_height="wrap_content"
+            android:layout_marginStart="@dimen/layout_horizontal_margin"
+            android:layout_marginTop="4dp"
+            android:layout_marginEnd="@dimen/layout_horizontal_margin"
+            android:text="@string/phone_book_perform_lookup"
+            android:visibility="gone"
+            app:layout_constraintStart_toStartOf="parent"
+            app:layout_constraintTop_toBottomOf="@+id/phoneBookFilterContainer"
+            tools:visibility="visible" />
+
+        <androidx.constraintlayout.widget.Barrier
+            android:id="@+id/phoneBookBottomBarrier"
+            android:layout_width="0dp"
+            android:layout_height="0dp"
+            app:barrierDirection="bottom"
+            app:constraint_referenced_ids="phoneBookSearchForMatrixContacts,phoneBookOnlyBoundContacts" />
+
         <View
             android:id="@+id/phoneBookFilterDivider"
             android:layout_width="0dp"
@@ -101,7 +122,7 @@
             android:background="?attr/vctr_list_divider_color"
             app:layout_constraintEnd_toEndOf="parent"
             app:layout_constraintStart_toStartOf="parent"
-            app:layout_constraintTop_toBottomOf="@+id/phoneBookOnlyBoundContacts" />
+            app:layout_constraintTop_toBottomOf="@+id/phoneBookBottomBarrier" />
 
         <androidx.recyclerview.widget.RecyclerView
             android:id="@+id/phoneBookRecyclerView"
diff --git a/vector/src/main/res/values/strings.xml b/vector/src/main/res/values/strings.xml
index 4f751a68d0..48729df815 100644
--- a/vector/src/main/res/values/strings.xml
+++ b/vector/src/main/res/values/strings.xml
@@ -2602,6 +2602,7 @@
     <string name="loading_contact_book">Retrieving your contacts…</string>
     <string name="empty_contact_book">Your contact book is empty</string>
     <string name="contacts_book_title">Contacts book</string>
+    <string name="phone_book_perform_lookup">Search for contacts on Matrix</string>
 
     <string name="three_pid_revoke_invite_dialog_title">Revoke invite</string>
     <string name="three_pid_revoke_invite_dialog_content">Revoke invite to %1$s?</string>