dissemination of public encryption certificates

[[e-mail] (Julien Pierre)]

Hi,

Since this is my first posting to this mailing list, let me introduce 
myself :

I'm a software engineer in AOL / Netscape and one of my responsibilities 
for several years has been to maintain the open source Netscape Security 
Services (NSS) library, which is used in the Mozilla browsers, many 
Netscape and Sun servers, and other internal products. The NSS library 
contains an implementation of S/MIME v3.

I was wondering what thoughts you may have on the following problem :

If I have a keypair and e-mail certificate, and I want to send encrypted 
e-mail to somebody knowing his e-mail address, what's a systematic way 
to obtain the recipient's encryption certificate ?

Traditionally today, signed e-mail messages typically contain the 
signer's public encryption certificate. However that means one party 
needs to first send a signed unencrypted, e-mail message to transmit the 
public encryption certificate before both parties can exchange encrypted 
messages.

There are also ways to find recipient certificates today using corporate 
directory servers, but users must know about them and manually configure 
them in their applications, and they are typically not widely available 
on the Internet.

I'm envisioning some standardized scheme where, by starting with the 
recipient's email address, it would be possible to locate a public 
directory server, then find the recipient's certificate by looking it up 
in that directory server.

My main question is : has any similar scheme been proposed ? I would 
rather work with something that exists, but if there is nothing that 
fits, I'm open to writing an RFC.

Also, what are the other ways that people locate recipient S/MIME e-mail 
encryption certificates ?

Thanks.