I'm a bit sleepy, so I'm trying to clarify:
Client has email@example.com which forwards to firstname.lastname@example.org.
Client sends mail with a return address of, what, email@example.com(?) and when someone@telus responds, it bounces? Where does the bounce occur? At the somehost.com server, or at the dreamhost server? Is her forwarding address also @telus?
I know there's a slightly similar issue with Gmail addresses, but I've not heard of this problem elsewhere: