ぷららメールが相手に届きません。

◆ぷららメールについて
メール送信後、送信相手から以下のメッセージが返ってきて、先方にメールが届きませんでした。どうすれば良いでしょうか、対応策がありましたら、ご教示くださいませ。
-----------------------------------------------------------
To: xxxxx@zzzz.plala.or.jp
From: Mail Administrator <Postmaster@plala.or.jp>
Subject: Mail System Error - Returned Mail with Subject: 確認のお願い
Date: Mon, 4 Mar 2024 19:05:09 +0900

This Message was undeliverable due to the following reason:
Your message was not delivered because the return address was refused.
The return address was "<xxxxx@zzzz.plala.or.jp>"
Please reply to <Postmaster@plala.or.jp>
if you feel this message to be in error.
______________________________________________________________________
Content-Type: message/delivery-status

Reporting-MTA: dns; msa14.plala.or.jp
Arrival-Date: Mon, 4 Mar 2024 19:05:08 +0900
Received-From-MTA: dns; xxxxyyyy.zzzz.plala.or.jp (223.218.109.148)

Final-Recipient: RFC822; <aaaaaa@outlook.jp>
Action: failed
Status: 5.1.1
Remote-MTA: dns; apc.olc.protection.outlook.com (104.47.58.161)
Diagnostic-Code: smtp; 550 5.7.1 Unfortunately, messages from [60.36.166.14] weren't sent. Please contact your Internet service provider since part of their network is on our block list (S3150). You can also refer your provider to http://mail.live.com/mail/troubleshooting.aspx#errors. [BN8NAM11FT077.eop-nam11.prod.protection.outlook.com 2024-03-04T10:05:09.460Z 08DC3BFD39475430]
_______________________________________________________p>
From: xxxxx@zzzz.plala.or.jp
Date: Mon, 04 Mar 2024 19:05:08 +0900
To: aaaaaa@outlook.jp
Subject: 確認のお願い
MIME-Version: 1.0
X-Mailer: AL-Mail32 Version 1.13
Content-Type: text/plain; charset=iso-2022-jp
X-VirusScan: Outbound; mvir-ac14; Mon, 4 Mar 2024 19:05:08 +0900

〇〇さん
（以下、略）

◆環境：　Windows11-PC
◆メーラー：　AL-Mail32 ver.1.13b

以上、よろしくお願いいたします。
(2024.3.13)


※OKWAVEより補足：「※OKWAVEより補足：「ＩＳＰぷらら」についての質問です。」についての質問です。