spam mail from my domain

our users often get spam mail saying that their email mailbox is full or password expired

how do i prevent them from receiving such emails ?

Authentication-Results: spf=pass (sender IP is 173.203.187.69)

smtp.mailfrom=savaari.com; myemaildomain.com.sg; dkim=none (message not

signed) header.d=none;myemaildomain.com.sg; dmarc=none action=none

header.from=myemaildomain.com.sg;

Received-SPF: Pass (protection.outlook.com: domain of savaari.com designates

173.203.187.69 as permitted sender) receiver=protection.outlook.com;

client-ip=173.203.187.69; helo=smtp69.iad3a.emailsrvr.com;

Received: from smtp69.iad3a.emailsrvr.com (173.203.187.69) by

AM1FFO11FD005.mail.protection.outlook.com (10.174.64.87) with Microsoft SMTP

Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA384_P384) id

15.20.820.5 via Frontend Transport; Tue, 5 Jun 2018 21:31:51 +0000

Received: from smtp33.relay.iad3a.emailsrvr.com (localhost [127.0.0.1])

by smtp33.relay.iad3a.emailsrvr.com (SMTP Server) with ESMTP id 5AF183A9D

for <hrdept@myemaildomain.com.sg>; Tue, 5 Jun 2018 17:31:50 -0400 (EDT)

Received: by smtp33.relay.iad3a.emailsrvr.com (Authenticated sender: ashley-AT-savaari.com) with ESMTPSA id D76FE54BD

for <hrdept@myemaildomain.com.sg>; Tue, 5 Jun 2018 17:31:46 -0400 (EDT)

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