diff --git a/Providers/MMFRestrictedCustomersServiceProvider.php b/Providers/MMFRestrictedCustomersServiceProvider.php
index a5a7b77..be69681 100644
--- a/Providers/MMFRestrictedCustomersServiceProvider.php
+++ b/Providers/MMFRestrictedCustomersServiceProvider.php
@@ -68,6 +68,19 @@ class MMFRestrictedCustomersServiceProvider extends ServiceProvider {
 			$priority = 20,
 			$arguments = 3
 		);
+
+		// Filter the list of Customers returned by MMFCustomersGroups when creating/editing a Customers Group.
+		Eventy::addFilter('mmfcustomergroups.groups.create.customers-query', function($customers_query) {
+			$user = auth()->user();
+			// Do not restrict the query if the current user is an admin.
+			if ( $user->role != User::ROLE_ADMIN ) {
+				// Get IDs of mailboxes the current user is allowed to access.
+				$mailboxes = $user->mailboxesIdsCanView();
+				// Restrict the query to the Customers the current user is allowed to access.
+				$customers_query->whereIn('customers.mailbox_id', $mailboxes);
+			}
+			return $customers_query;
+		});
 	}
 
 	/**