External certificate sources can be used if the communication partner has an LDAP directory with correspondingly stored S/MIME certificates for the users.
Both the Employment Agency and, for example, the Bavarian Lawyers' Court provide a PKI interface for this purpose.
You will receive the connection parameters to be adapted from your communication partner.
The domain list must contain a list of domains for which the communication partner provides certificates.
Use the "Test settings" button to check whether a certificate can be found for a certain address and whether the access data are correct.