Yes, this is not exploitable without vulnerable bash.

But to paraphrase from the thread:

However, qmail is not parsing mail from:<> and rcpt to:<> in accordance with RFC821/RFC2821. Almost anything is allowed between the <>. There is no reason that qmail should allow the string "() { :; }; nc -e /bin/bash localhost 7777" to ever pass through mail from:<> or rcpt to:<>, and thus into the environment, in the first place.

While the manpage does say what you pasted above, there's a difference between "may contain special characters" and "may contain anything the user puts in this part of the SMTP dialog".