There is a bug for FCC-ed messages in Emacs 18.58 where it adds a timezone on the "From " line after the year instead of before the year. (Before it didn't add the timezone at all.) This is incompatible with the standard format for the "From " line, and RMAIL in particular can no longer distinguish between the messages. Karl Berry <karl@cs.umb.edu>, Felix Lee <flee@cs.psu.edu>, Nick Gianniotis <nico@japan.sbi.com> and many others have all posted patches for this. Karl's is the simplest and just stops Emacs from adding the timezone:
>*** ./ORIG/sendmail.el Tue Jan 28 16:22:56 1992 >--- ./sendmail.el Thu May 14 18:23:48 1992 >*************** >*** 285,287 **** > (insert "\nFrom " (user-login-name) " " >! (current-time-string) " " timezone "\n") > (insert-buffer-substring rmailbuf) >--- 285,287 ---- > (insert "\nFrom " (user-login-name) " " >! (current-time-string) "\n") > (insert-buffer-substring rmailbuf)