Emails being blocked by Gmail from office 365

Anonymous
2023-03-02T23:25:26+00:00

When the emails is sent to gmail its being blocked stating

Delivery has failed to these recipients or groups:

___@___.___ (***********@gmail.com)

Your message wasn't delivered because the recipient's email provider rejected it.

all my records are up to date..

gmail.com suspects your message is spam and rejected it.

natasha.daniel Office 365 gmail.com
Sender Action Required
<br> --- --- --- --- ---
Messages suspected as spam
How to Fix It
Try to modify your message, or change how you're sending the message, using the guidance in this article: Bulk E-mailing Best Practices for Senders Using Forefront Online Protection for Exchange. Then resend your message.
If you continue to experience the problem, contact the recipient by some other means (by phone, for example) and ask them to ask their email admin to add your email address, or your domain name, to their allowed senders list.

Was this helpful?Send feedback to Microsoft.

More Info for Email AdminsStatus code: 550 5.7.350

When Office 365 tried to send the message to the recipient (outside Office 365), the recipient's email server (or email filtering service) suspected the sender's message is spam.

If the sender can't fix the problem by modifying their message, contact the recipient's email admin and ask them to add your domain name, or the sender's email address, to their list of allowed senders.

Although the sender may be able to alter the message contents to fix this issue, it's likely that only the recipient's email admin can fix this problem. Unfortunately, Office 365 Support is unlikely to be able to help fix these kinds of externally reported errors.

Original Message Details

Created Date: 3/2/2023 11:29:38 PM
Sender Address: *********@*****.com
Recipient Address: *********@gmail.com
Subject: Email check

Error Details

Reported error: 550 5.7.350 Remote server returned message detected as spam -> 550 5.7.1 [2a01:111:f403:700f::715 19] Our system has detected that this;message is likely suspicious due to the very low reputation of the;sending domain. To best protect our users from spam, the message has;been blocked. Please visit; https://support.google.com/mail/answer/188131 for more information. c23-20020aa7c997000000b004ace5dc6b61si945041edt.369 - gsmtp
DSN generated by: PN3P287MB0113.INDP287.PROD.OUTLOOK.COM
Outlook | Windows | Classic Outlook for Windows | For home

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  1. Anonymous
    2024-03-04T19:32:32+00:00

    Hi Michael,

    In our case the DMARC record was set p=quarantine before the issues started but of course we had a confirmed leak and the domain reputation was affected. For the first week 50% of emails sent via IPv4 would fail based on domain reputation whereas IPV6 would fail every message. Week 2-4 email sent via ipv6 would be still rejected for domain reputation where as ipv4 would be accepted.

    I still think something is off with the IPv6 google mail servers as the results are clearly not consistent. As most senders still use IPv4 I think it's a volume related issue with the algorithm.

    That said I'm all for DMARC records! In fact we need to push for DMARC + DKIM only and drop SPF but... step 1 DMARC.

    @XavierCho: IPv6 reverse lookup issue... interesting point I'll need to check that out

    Br.

    Joshua

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  2. Anonymous
    2024-03-03T22:21:05+00:00

    Hi Guys,

    Just to be clear, if you find yourself in this situation

    1. You have an SPF record correctly setup with only the providers you need
    2. DMARC setup with strong enforcement to reject bad SPF/DKIM
    3. Perfect reputation with Google, no spam or reports against the domain
    4. Google (and google related domains) are rejecting your emails.

    a, The email from Google shows the rejected headers, in these headers

    i. The source address is an IPv6 address.

    ii. The rejection headers indicate that the email source address could not be validated against your SPF

    If the above is true for you, then you may be experiencing the issue where a MS IPv6 address is not being resolved correctly as a MS email server.

    If you want to confirm this is the case for your, grab the source address from the email headers, perform a IPv6 reverse lookup, if it doesn't resolve to *.protection.outlook.com, then you have the source address issue.

    This causes Google to mark the email as being spoofed and you will get the rejection. The wording on the email response from Google is slightly misleading.

    If this is your situation, creating connectors to force Microsoft to send the emails using IPv4 will resolve the issue, because the IPv4 address seem to resolve correctly.

    Absolutely important to have SPF and DKIM setup correctly, I do recommend to do that first to make sure these are correct, if you still have the issues then try using connectors.

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  3. Ron-6928 4,991 Reputation points
    2024-03-01T18:17:04+00:00

    It sounds like the issue you had was specific to the incorrect SPF record; where spammers were able to send as your domain. That caused you to get flagged by gmail.

    Yup. Invalid or missing SPF resulting in spammers spoofing his domain name to spam others. I have been monitoring all posts about this issue (Yahoo/Gmail bounce backs) and not all of them are DMARC related. Some have multiple SPF records which causes it to "break" or become invalid. Most of them do not have both or all records (SPF, DMARC, DKIM).

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  4. Anonymous
    2024-03-01T17:36:15+00:00

    ** Update **

    The original issue of emails sent via O365 Exchange to Gmail and Yahoo not being delivered was a pre-cursor to them requiring changes to DNS.

    If you did not have a DMARC record published for your sending domain, you were affected and your email stopped. When this first started and was not widely known that they made those changes, it was possible to force O365 Exchange email to be routed thru an SMTP connector.

    However, now that the requirements have been published by them and "well known" , all that needs to be done is add a DMARC record into your domains DNS. (SPF and SenderID records should already be in there)

    https://dmarcian.com/yahoo-and-google-dmarc-required/

    Michael B. Morell, CISSP #431307 CCSK (he/him/his/sir)

    DirectionWeb

    Owner and Information Security Professional

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  5. Anonymous
    2024-03-01T17:29:51+00:00

    The issue now appears to be the requirements by Gmail/Yahoo, to have DMARC records published in DNS for your domain.

    https://dmarcian.com/yahoo-and-google-dmarc-required/

    Once you add the dmarc records in, your email should begin being delivered.

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