mh-show-maximum-size

mh-show-maximum-size is a variable defined in `mh-e.el'.
Its value is

0

Documentation:
*Maximum size of message (in bytes) to display automatically.

This option provides an opportunity to skip over large messages
which may be slow to load. The default value of 0 means that all
message are shown regardless of size.

You can customize this variable.

This variable was introduced, or its default value was changed, in version 8.0 of the MH-E package that is part of Emacs 22.1.