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Messages blocked by Barracuda, SPF failures

Anonymous
2021-08-11T14:57:19+00:00

Over the last few days we have had a number of emails bounce back, all from customers utilizing barracuda. When checking the headers, all of the bounced messages are from a series of ipv6 addresses, that are not listed on microsoft's ip listing for office365, and I suspect that is why our SPF is failing. IP addresses that we are seeing are 2603:10b6:5:395::23, 2603:10b6:404:103::9, and some others all in the same series. I know they belong to Microsoft, but don't seem to be registered with spf.protection.outlook.com. Is there another include that I should have in our SPF to cover these additional addresses?

The returned NDR is the same for all.

550 5.7.350 Remote server returned message detected as spam -> 550 permanent failure for one or more recipients

Our spf: v=spf1 ip4:[internal-ip] ip4:[internal-ip] ip4:[internal-ip] include:spf.protection.outlook.com -all

Microsoft 365 and Office | Subscription, account, billing | For home | Windows

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  1. Anonymous
    2021-08-11T20:27:06+00:00

    We do not use barracuda. Barracuda is rejecting our emails that we are sending from office365. We have had SPF, DKIM, and DMARC configured for quite a while, and the issue just started last week, and the only common failure is the SPF and the ipv6 addresses associated with those messages. As I am not a barracuda customer, they will not provide any support.

    Really unsure where to proceed from here. I've spoken to office365 support, and they all ignore the common question regarding the ip address. The addresses of failure are not listed on the office365 ip address page (Office 365 URLs and IP address ranges - Microsoft 365 Enterprise | Microsoft Docs) which is why I question if that is causing the failure.

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  2. Anonymous
    2021-08-22T08:38:19+00:00

    Hi Timothy,

    Is there anything else I can do to help?

    Please let me know if you need further assistance.

    Regards,

    Mac

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  3. Anonymous
    2021-08-17T08:12:14+00:00

    Hi Timothy,

    Regarding this situation seeing that you can not get support from barracuda, could you please perform a test with one of recipient and have him add you in his allow list and confirm if you still get a NDR when sending the email. if not the issue will need to be fixed from the recipient side.

    Please let me know your findings.

    Regards,

    Mac

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  4. Anonymous
    2021-08-11T18:13:24+00:00

    Hi Timothy,

    Greetings.

    Thank you for raising your concern in this community.

    There are different reason for this error code, such as:

    • The message is too large
    • The subject line is too large
    • Messages suspected to be spam
    • Incomplete DNS record. ( SPF, DKIM and DMARC)

    Now regarding the SPF, seeing that it is related to barracuda, could you check your sender policy framework in barracuda, In short your Barracuda configuration.

    Please let me know your findings after that.

    Regards,

    Mac

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