ORA-24247 with valid ACL when sending smtp mail

I have users with the same privileges to the same ACL and some can send emails and some others cannot !

In principle I created the ACL for USER1:

BEGIN
dbms_network_acl_admin.create_acl
 (acl  => 'mails_senden.xml',
  description => 'Mails senden ueber INTRANET Mail-Server ...',
  principal => 'USER1',
  is_grant => true,
  privilege => 'connect');
COMMIT;
END;
/
BEGIN
dbms_network_acl_admin.assign_acl
 (acl  => 'mails_senden.xml',
  host  => 'xx.xx.x.xx',
  lower_port => null,
  upper_port => null);
COMMIT;
END;
/
BEGIN
dbms_network_acl_admin.add_privilege
 (acl  => 'mails_senden.xml',
  principal => 'USER1',
  is_grant => true,
  privilege => 'resolve');
COMMIT;