my $labels = Mail::Box::MH::Labels->new; $labels->read(...) $labels->write(...)
See SYNOPSIS in Mail::Reporter
MH type message folders use one dedicated file per folder-directory to list special tags to messages in that folder. By doing this, mail agents may avoid parsing all the messages, which is very resource consuming.
Labels can be used to group messages, for instance to reflect which messages have been read or which look like spam. Some labels are predefined, but more can be added without limitation.
See DESCRIPTION in Mail::Reporter