I'm sure he's talking about something like the hundreds of web frontends to POP3 or IMAP and SMTP servers that are written in PHP or perl or whatever, but in Common Lisp instead.
I don't believe there is one, as yet. I'm using Squirrelmail myself, and would love to switch to something lisp-based.
If you find (or write) one before I get around to writing mine, I'd love to hear about it Mel-base and Hunchentoot do look like a good pair of pillars to start with, though, along with CL-WHO.