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Spam checking issue with IPv6
Problem reported by Kayasidh Kasyapanun - Today at 8:24 PM
Submitted
K
We've seen problems with senders whose originating their mails with IPv6 such as outlook.com
SPF and Reverse DNS fail to check for those mails. Here is an example.

THIS IS THE MAIL HEADER
Received: from TYPPR03CU001.outbound.protection.outlook.com (mail-japaneastazon11022097.outbound.protection.outlook.com [52.101.126.97]) by ourmailgateway with SMTP;
   Thu, 19 Mar 2026 09:45:33 +0700
Received: from JH0PR01MB6874.apcprd01.prod.exchangelabs.com
 (2603:1096:990:7d::10) by TYZPR01MB6076.apcprd01.prod.exchangelabs.com
 (2603:1096:405:78::11) with Microsoft SMTP Server (version=TLS1_2,
 cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.9723.19; Thu, 19 Mar
 2026 02:45:07 +0000
Received: from JH0PR01MB6874.apcprd01.prod.exchangelabs.com
 ([fe80::6ed5:f3a1:6d2a:c04e]) by JH0PR01MB6874.apcprd01.prod.exchangelabs.com
 ([fe80::6ed5:f3a1:6d2a:c04e%5]) with mapi id 15.20.9723.018; Thu, 19 Mar 2026
 02:45:07 +0000
THIS IS SPAM CHECK LOG
[2026.03.19] 09:45:41.087 [17277862] Spam check args: from: sender@thedomain; messageID: 17277862; messagePath: C:/SmarterMail/Spool/SubSpool5/17277862.eml; sender: sender@thedomain; sendersDomain: thedomain; sendersIp: fe80::6ed5:f3a1:6d2a:c04e; returnPath: sender@thedomain; sendersEhlo: TYPPR03CU001.outbound.protection.outlook.com
[2026.03.19] 09:45:41.154 [17277862] [fe80::6ed5:f3a1:6d2a:c04e] No valid reverse DNS entry found.
[2026.03.19] 09:45:41.250 [17277862] Running SPF check
[2026.03.19] 09:45:41.328 [17277862] SPF Fail. IP: fe80::6ed5:f3a1:6d2a:c04e, Sender: sender@thedomain, FailReason: [no matches for fe80::6ed5:f3a1:6d2a:c04e]; all result of Fail observed

I have to lower SPF and Reverse DNS scores to allow these good mails to arrive.

How can I fix this?

Thank you in advance.
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