SYNOPSIS

 my $subset = Mail::Message::Head::Subset->new(...)
 $subset->isa('Mail::Message::Head')  # true
 $subset->guessBodySize               # integer or undef
 $subset->isDelayed                   # true

See SYNOPSIS in Mail::Message::Head

DESCRIPTION

Some types of folders contain an index file which lists a few lines of information per messages. Especially when it is costly to read header lines, the index speeds-up access considerably. For instance, the subjects of all messages are often wanted, but waiting for a thousand messages of the folder to be read may imply a thousand network reads (IMAP) or file openings (MH)

When you access header fields which are not in the header subset, the whole header has to be parsed (which may consume considerable time, depending on the type of folder).

See DESCRIPTION in Mail::Message::Head

DETAILS

Ordered header fields

See Ordered header fields in Mail::Message::Head

Head class implementation

See Head class implementation in Mail::Message::Head

Subsets of header fields

See Subsets of header fields in Mail::Message::Head