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Om Joshi
Flag for United Kingdom of Great Britain and Northern Ireland asked on

Exchagne rejecting email with error 550 5.7.1 Recipient not authorised. your IP has been found block listed

I am stuck with this issue for long and trying to find a solution

many spam emails get through to existing mail boxes in exchange but some genuine work related emails senders complain about below mentioned error

"550 5.7.1 recipient not authorized, your IP has been found block listed"

when I check the SMTP receive log i see that recipient email address is known he/she is a existing user in the organization.

I am wonder the reason why exchange is throwing such error when its recipient and sender both are genuine and do not contain spam or meet the SPAM criteria.

awaiting prompt response on my query.


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Simon Butler (Sembee)

8/22/2022 - Mon

Please check IP black listed as per the error here: http://www.mxtoolbox.com/blacklists.aspx

Om Joshi

One of the thing  i came to know doing trouble shotting  is RDNS querry and my ISP can't provide RDNS to my ip.

but it shouldn't reject emails from some global organisations and let through spams.

awaiting reply.
Simon Butler (Sembee)

The NDR that you have posted isn't default. Therefore it has been configured within Exchange or a third party product.
If you are using a blacklist provider in Exchange then you can disable it - it is part of the antispam options which you should see in EMC.
If those aren't enabled then it has to be a third party product doing the blacklisting.

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Om Joshi

Hi Simon,

I haven't installed any thrid party antispam. Although I have installed Symantec Endpoint Protection but it has no exchange feature in the product.

Please find attached my anti-spam settings on my exchange 2007.

My sender reputation settings were on 7 and i have changed it to 6 while looking at this post as a  matter of suspicion.

please see what do you think my anti spam config should be as i do not have thrid party anti-spam and relied on exchange due to funds issue.

awaiting your reply.

Simon Butler (Sembee)

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Om Joshi


I understand but not quiet 100%. is there any other place where i can get more detailed information. Also what is the best practice.

one more thing puzzels me is What happens  if user from my organisation sends an email to the person he / she receives quiet smoothly and sometimes recipient's replies get bounced so wondering why sometimes.

awaiting reply with valuable comments.
Simon Butler (Sembee)

Best practise? No such thing.
If you are deploying blacklists then you should really give senders as much information as possible on why they are blacklisted. A spammer isn't going to see (or care). Did you not setup the server and the blacklisting? It isn't something that should be done without full consideration and it is highly unusual to use multiple blacklists - most people stick with just one or two.

As for why emails can sometimes get bounced, any number of reasons. It could be that the sender emails can take a number of different routes and the one that is used that time is blacklisted and others are not. Not a huge amount you can do about it - if you use blacklists then you are depending on them being accurate.

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