Example of this function output:
<?php
$parse = mailparse_msg_parse_file('mail.txt');
print_r(mailparse_msg_get_structure($parse);
?>
Output will be:
Array
(
    [0] => 1
    [1] => 1.1
    [2] => 1.1.1
    [3] => 1.1.2
    [4] => 1.2
)(PECL mailparse >= 0.9.0)
mailparse_msg_get_structure — Returns an array of mime section names in the supplied message
mimemail
       A valid MIME resource.
      
Example of this function output:
<?php
$parse = mailparse_msg_parse_file('mail.txt');
print_r(mailparse_msg_get_structure($parse);
?>
Output will be:
Array
(
    [0] => 1
    [1] => 1.1
    [2] => 1.1.1
    [3] => 1.1.2
    [4] => 1.2
)