diff --git a/src/main/java/net/hostsharing/hsadminng/hs/office/contact/HsOfficeContactRbacRepository.java b/src/main/java/net/hostsharing/hsadminng/hs/office/contact/HsOfficeContactRbacRepository.java
index 924f3277..ec2b15d1 100644
--- a/src/main/java/net/hostsharing/hsadminng/hs/office/contact/HsOfficeContactRbacRepository.java
+++ b/src/main/java/net/hostsharing/hsadminng/hs/office/contact/HsOfficeContactRbacRepository.java
@@ -35,6 +35,7 @@ public interface HsOfficeContactRbacRepository extends Repository<HsOfficeContac
     }
 
     static String emailRegEx(@NotNull String emailAddress) {
+        // TODO.impl: find more secure solution, maybe we substitute a placeholder with the whole expression?
         if (emailAddress.contains("'") || emailAddress.endsWith("\\") ) {
             throw new ValidationException(
                     "emailAddress contains invalid characters: " + emailAddress);