mh-large-folder

mh-large-folder is a variable defined in `mh-e.el'.
Its value is

200

Documentation:
The number of messages that indicates a large folder.

If a folder is deemed to be large, that is the number of messages
in it exceed this value, then confirmation is needed when it is
visited. Even when `mh-show-threads-flag' is non-nil, the folder
is not automatically threaded, if it is large. If set to nil all
folders are treated as if they are small.

You can customize this variable.

This variable was introduced, or its default value was changed, in version 7.0 of the MH-E package that is part of Emacs 22.1.