so now i have make a new blank installation of SmarterMail and Linux 

ubuntu-22.04.5-live-server-amd64

SmarterMail Version: 9245

add a new Authentication Provider LDAP is working

import Acounts from Authentication Provider LDAP is working

then i make an Update SmarterMail Version: 9245 to 9280

add a new Authentication Provider LDAP is working

import Acounts from existing and new Authentication Provider LDAP is working

then i make an relese upgrade from Ubunto to 24.04

   New release '24.04.2 LTS' available.
   Run 'do-release-upgrade' to upgrade to it.

add a new Authentication Provider LDAP is NOT working

import Acounts from existing Authentication Provider LDAP is NOT working

so i think its a fakt:

Authentication Provider LDAP is working on Ubuntu 22.04

Authentication Provider LDAP is NOT working on Ubuntu 24.04

Thanks for reporting this Markus, I believe there was in fact a change in the ldap provider between these two versions of Ubuntu. We'll work on getting this confirmed in-house and escalated for you. 

Hey Markus! After posting my response here yesterday I checked in with Ray (in Support here) as I vaguely remembered him having run into this previously. We did  a little research on the development escalation at the time and it looks like this was found to be an issue with the ldap DLL version in use in .NET on Linux, rather than an issue with SmarterMail specifically. 

The Microsoft .NET hub pages discussing the issue at the time seemed to indicate Microsoft wasn't planning on resolving it either, so their recommended workaround is downgrading to the ldap DLL version used in the previous version. I believe Ray had some luck doing so but the process for getting that implemented might vary depending on your versions. 

From what I understand you just need to manually install and reference the LDAP DLL 2.5 instead of 2.6. This is discussed in more detail here where an admin had a similar issue under a different product: https://askubuntu.com/questions/1540581/libldap-2-5-on-ubuntu-24-04