'n' is not a command here but a reply to "Postpone?" question.
macro index,pager <Esc>s \
"<Enter><exit><pipe-message>spamassassin -d | ~/mail/bin/spamcop.py<Enter><next-undeleted>"
macro index,pager <Esc>z \
- "<Enter><exit>:set editor='vim -s ~/mail/misc/spamcop.vim'<Enter><reply>:set editor=vim.sh<Enter><exit><next-undeleted>"
+ "<Enter><exit>:set editor='vim -s ~/mail/misc/spamcop.vim'<Enter><reply>:set editor=vim.sh<Enter><exit>n"
# Go to main mailboxes
macro index,pager H <Enter><exit><Home><change-folder>!<Enter>