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Gordon Tin
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How can I stop spam emails which contains proper MX, A, TXT SPF??


1. Exchange2016

2. Symantec Mail Security for Microsoft Exchange

      transportagents including sender ID installed

Recently, we received spam from MANY .co domain. After checking, it is noticed that 

domains are with properly MX, A, TXT SPF records and MX is from google. 

So this spam email look like normal email.

Any idea how I can stop this kind of spam emails?

SecurityMicrosoftExchange* Spam blockers* spam filter

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Last Comment
Gordon Tin

8/22/2022 - Mon
David Favor

The fix is to do these checks, the refuse submission/acceptance of any email that fails any test.

1) IPrev

2) SPF DNS record missing

3) SPF failure

4) DKIM DNS record missing

5) DKIM Signature missing in message

6) DKIM Signature failed in message (message has changed or has incorrect/bogus signature)

7) DMARC - If DMARC record is configured correctly, return a DMARC report to sender about problem(s) encountered.

8) In SMTP response, clearly state problem. You'll have to determine if you return a 4XX (give them time to fix the problem) or 5XX (they must fix their problem + arrange to do a resend).
Dr. Klahn

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It seems what you are looking for us content based filtering
Look at the Symantec mail security option to see whether you can develop a pattern, or whether it includes statistical type of content analysis (Bayesian)
You would need to check which options you currently have enabled.
Gordon Tin

I finally blocked all .co and exception for wanted .co domain
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