Why is the sender's address in the header PHPmailer on Yandex mail not correct?

Question

PHP

Hello
There is a domain mail on Yandex mx servers I
send mail through the phpmailer class via smtp Yandex mail.
Letters are sent normally, but in the header the address of the sender is localhost (127.0.0.1)
Why is this happening?
Perhaps due to the fact that the server has IP6 in addition to IP4?
How then to configure?
Email header example:

Received: from smtp4m.mail.yandex.net (smtp4m.mail.yandex.net [77.88.61.131])
  by forward11m.cmail.yandex.net (Yandex) with ESMTP id C45DA2066F
  for <****@bk.ru>; Sun, 12 Jun 2016 02:09:19 +0300 (MSK)
Received: from smtp4m.mail.yandex.net (localhost [127.0.0.1])
  by smtp4m.mail.yandex.net (Yandex) with ESMTP id A60F2BE0003
  for <****@bk.ru>; Sun, 12 Jun 2016 02:09:19 +0300 (MSK)
Received: by smtp4m.mail.yandex.net (nwsmtp/Yandex) with ESMTPSA id KVf3mzMHF5-9JYaYUWF;
  Sun, 12 Jun 2016 02:09:19 +0300
  (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits))
  (Client certificate not present)

Answer 1

This is a header added by Yandex for some kind of internal routing, for example, when sending a letter to a spam filter, it has nothing to do with your server settings.