In fact, the trace doesn't show it, but I have an alternate domain name in the certificate, and the CN is set to the FQDN of the server (without that, OpenLDAP doesn't start), so if you look at the successful connection, the host and certificate are the same, and it works ...You are connection to host ldap.domain.com
/C=FR/ST=Lorraine/L=Nancy/O=<hiddencompany>/OU=<hiddencompany>/CN=smtp.<hiddendomain>.com/emailAddress=it@<hiddendomain>.com,
but the certificate is issued to host smtp.domain.com, a certificate verification must fail.
Thanks for your answer ...
Best regards
Denis