See Mail::Message::Body
if($body->isNested) {
my $nest = $body->nested;
$nest->delete;
}
See SYNOPSIS in Mail::Message::Body
The body (content) of a message can be stored in various ways. In this
manual-page you find the description of extra functionality you have
when a message contains a nested message, like message/rfc822.
A nested message is different from a multipart message which contains
only one element, because a nested message has a full set of message
header fields defined by the RFC882, where a part of a multipart has
only a few. But because we do not keep track whether all fields are
presented, a Mail::Message::Part is used anyway.
See DESCRIPTION in Mail::Message::Body