Why you might want to use the DFN-PKI LDAP Server:

If the recipient of an encrypted e-mail also has a DFN-PKI user certificate (most higher education facilities in Germany do), then you can send this encrypted e-mail without a prior handshake, i.e. exchange of digitally signed e-mails.

You define a new Address Book.

Your new address book is a LDAP Server.

The Servername is "ldap.pca.dfn.de"

This is just informing you that you need to restart Outlook, clicking on "OK" doesn't do it. You need to manually restart Outlook before you can use the new Address Book.

This tells Outlook to use a secure connection to the LDAP Server. With "Anzeigename" you name your LDAP address book, e.g. "ldap-DFN-PKI".With "Anschluss" you define your TCP Port to the LDAP Server, the value "636" enforces a secure connection.

Here you define the scope of your search within the LDAP (directory structure). Your widest search scope can be "ou=DFN-PKI,o=DFN-Verein,c=de".

You are trying to send an encrypted e-mail, and decide to look up the recipient in the DFN-PKI LDAP address book.

You specify that your search should be inside the ldap-DFN-PKI address book and you want to make an extended search.

You search criterium is "RWTH RA" anywhere inside the "Common Name" field of the DFN-PKI user certificates.

You have found the recipient you are looking for, you need to save them as your own contact.

Please note the user added "(DFN)" part in the Name. This helps you distinguish your contact as one imported from the DFN-PKI LDAP address book, i.e. with a user certificate (and a public RSA Key associated to it).

You're back to wanting to send an encrypted e-mail, to the contact you previously explicitly found in the DFN-LDAP address book and saved as your "own" contact.

You need to search among your own "Contacts", because you can only send an encrypted e-mail to an "own" contact, choose the one you tagged with "(DFN)".

Choose to "encrypt".