Вы должны использовать курсор из того, что я могу сказать (если не считать загрузки всего).
<?php
/* $this is a class that extends SoapClient using the groupwise.wsdl */
$q = (object)[
'folderType' => 'Mailbox',
'view' => 'count unreadCount'
];
$folder = $this->getFolderRequest($q);
$q = (object)[
'container' => $folder->folder->id,
'view' => 'subject peek noDownload'
];
$cursor = $this->createCursorRequest($q);
$q = (object)[
'container' => $data->folder->id,
'cursor' => $cursor->cursor,
'position' => 'end',
'count' => 20,
'forward' => TRUE
];
$msgs = $this->readCursorRequest($q);
var_dump($msgs);
/* You could also throw readCursorRequest() in a loop and track offset + position for more intensive purposes */
?>
Подробнее: https://www.novell.com/documentation/developer/groupwise_sdk/gwsdk_gwwebservices/data/b7m3i3x.html