DMARC - gmail.com or is it yahoo.com

[cyg Simple <cygsimple@gmail.com>]

I find this excerpt from cygwin-help a bit confusing.  Notice the
"yahoo.com" in the "Remote host said:" message.  What's really going on
here?  Why is yahoo.com doing the authentication for a gmail.com address?

<excerpt>
Received: (qmail 130602 invoked for bounce); 17 Nov 2016 10:26:04 -0000
Date: 17 Nov 2016 10:26:04 -0000
From: MAILER-DAEMON@sourceware.org
To: cygwin-return-205832-@cygwin.com
Subject: failure notice

Hi. This is the qmail-send program at sourceware.org.
I'm afraid I wasn't able to deliver your message to the following addresses.
This is a permanent error; I've given up. Sorry it didn't work out.

<cygsimple@gmail.com>:
User and password not set, continuing without authentication.
<cygsimple@gmail.com> 173.194.202.27 failed after I sent the message.
Remote host said: 550-5.7.1 Unauthenticated email from yahoo.com is not
accepted due to domain's
550-5.7.1 DMARC policy. Please contact the administrator of yahoo.com
domain if
550-5.7.1 this was a legitimate mail. Please visit
550-5.7.1  https://support.google.com/mail/answer/2451690 to learn about the
550 5.7.1 DMARC initiative. e69si30940847pfk.231 - gsmtp
</excerpt>

-- 
cyg Simple

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