ah HA!  Found it!

From the Fanfic ML FAQ:


* HOW DO I SUBSCRIBE/UNSUBSCRIBE TO THE ML?

To SUBSCRIBE to the mailing list, send an email message with the word 
[subscribe] in the [Subject:] field to [fanfic-request@fanfic.com].

Example:
 
 To: fanfic-request@fanfic.com
 Subject: subscribe
 
To UNSUBSCRIBE from the mailing list, simply send a message with the
word 
[unsubscribe] in [Subject:] field to [fanfic-request@fanfic.com].

Example:
 
 To: fanfic-request@fanfic.com
 Subject: unsubscribe
 


Hope this helps....

-joyce, Disciple of Kasumi and Belldandy