my $index = Mail::Box::MH::Index->new; $index->read(...) $index->write(...)
See SYNOPSIS in Mail::Reporter
Message folders which store their data in one single file per message are
very inefficient for producing subject overviews and for computing message
threads. The Mail::Box::MH::Index
object is able to store and read a the
headers of a set of Mail::Box::MH::Message
messages which are
part of a single Mail::Box::MH
folder in one file.
When the Mail::Box::MH::Index
functionality is enabled by specifying
Mail::Box::MH::new(keep_index) when opening a folder, the index file
is automatically read. When the folder is closed, a new index file is
created.
Special care is taken to avoid problems which occur when the user changes or removes message files without updating the index. If the index is not trustworthy it will not be used (costing some performance for the reader of the folder).
See DESCRIPTION in Mail::Reporter