"Read the overview of GROUP and build the map."
(when (file-exists-p (nnweb-overview-file group))
(with-temp-buffer
- (mm-insert-file-contents (nnweb-overview-file group))
+ (nnheader-insert-file-contents (nnweb-overview-file group))
(goto-char (point-min))
(let (header)
(while (not (eobp))