Mail delivery system

[b2027642]

I am facing few issues with email notification on my magento site.

The problem is that either admin and customer won't receive any order conformation email. The order goes through fine but no one gets a email conformation of order.

Also admin keep receiving the Mail delivery failed: all the time when user subscribes to a news letter.

but there no sign of email confrontation.

 I would be grateful if anyone could suggest something that could resolve this issue.

THANKS

Here's the error below:

This message was created automatically by mail delivery software.

A message that you sent could not be delivered to one or more of
its recipients. This is a permanent error. The following address(es)
failed:
email@yahoo.com:
SMTP error from remote server for TEXT command, host: mta7.am0.yahoodns.net () reason: 554 5.7.9 Message not accepted for policy reasons.  See https://help.yahoo
.com/kb/postmaster/SLN7253.html



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    id 0M7z2j-1cmZXo0JdJ-00vfOp; Thu, 27 Oct 2016 21:55:25 +0200
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Message-Id: <zLKyET-1cy9Jr3pol-018Ndh@infong-uk78.kundenserver.de>
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To: =?utf-8?B?ZmVyaV9iZW5p?= <email@yahoo.com>
Subject: =?utf-8?B?TmV3c2xldHRlciBzdWJzY3JpcHRpb24gY29uZmlybWF0aW9u?=
From: Sales <email@yahoo.com>
Date: Thu, 27 Oct 2016 19:55:24 +0000
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