Trying to find help for 550 5.7.511 Access denied, banned sender

Copper Contributor

I run a mail server for many business clients of mine. Microsoft have blocked our IP address, so we cant send to Office365 email addresses. I get a bounce back saying:


said: 550 5.7.511 Access denied, banned sender[]. To request
removal from this list please forward this message to delist [at] For more information please go to AS(1410)
[] (in reply to RCPT TO


(I have changed my server IP above)


So I emailed delist[at] but they said:

"I do not see anything offhand that would be preventing your mail from reaching our customers for the following IP : ("


And gave me various links to pages with different support channels. One of them was to login to or something, but I cant do that as I dont have an account. 


One of them was contact Microsoft support and they said its not to do with them, contact Office365. 


So I filled in a form on and they replied:

"The IP address in question is not currently blocked in our system. Please refer to the email message you received from Microsoft and follow the steps it suggests." - which I have done, with the first email above!


I also filled in the form for emailing Live, Hotmail, and got no reply but dont think its to do with them. 


So I am very confused at the moment with all the different support channels, various Microsoft support telling me they cant see a reason for the block and then doing no more about it. 


I have no idea what the correct channel is and how to fix this, does anyone know? Its a bit of a shambles Microsofts side of it to be honest. 




35 Replies
We have the same problem!
We can't send mails to Microsoft 365 Exchange, but,,, it's ok!

@suportecw We have the same problem too.  I've requested delisting via the website but it responds there is no listing for the involved IP.  Next try is send the error message to Email address removed -> but according to the automated response it can take up to 24h 


MS found a great way to increase their marketshare it appears ...

@timbertens this problem is occurring since last Tuesday! Our mail server is Zimbra ZCS, and we have approximately 1200 accounts, that can't send mails to MS 365 Exchange... We are having some troubles and loss with this :\

Yes started last Tuesday for me too. First time I knew about it was 7:30am GMT.

Did anybody see some progress in this? At our side IP's are still blocked and no reaction from Microsoft

I have a Microsoft support engineer helping me. He emails and calls often. So it’s good there is someone BUT I don’t understand why they can’t find the problem. He keeps asking for me “try again” but it’s not fixed. They can’t see my IP in a blocklist. It’s very strange but also unbelievable no one at Microsoft can find the reason. We’re on the 3rd day of blocks now and due to Christmas I doubt it’s a priority for them.

Having same issue for the past 7 days. I took a new server in a different data center and moved some of the accounts over to the new server, but that did not resolve the issue, still blocked and banned from sending to office365 users. Been in the loop many times by sending emails, or filling forms for microsoft support, but I am not receiving any useful info. After delisting, I get a message that our IP is not blacklisted, so why aren't our emails working?
Anyone with a solution, please help.
We are having the same problem since 22 December. This needs to be resolved.
Are all of your servers facing this problem hosted on Linode? Ours are.... If so, please submit a ticket to the friendly people at Linode too. I hope that if there are enough tickets they will reach to MS at a higher level that they currently have and it gets solved quicker
No my other linodes are sending mail via a php script to Microsoft ok. It’s just this one linode server I use for email accounts.

@timbertens I have contacted Linode multiple times on this issue. To be honest, I am disappointed with their response. It seems there is nothing they can do.


I'm also not really getting anywhere with Microsoft so far. Hopefully this issue is now being escalated.

9 days and Microsoft doesn't answered us... The problem persist and we can't do anything to resolve it =/
I do have someone replying to me. They just have not been able to solve it. They have escalated it.

I have sent them a link to this thread and the other one above, so inform them others have the same issue originating about the same time.

In the meantime as I have my own mail server with Postfix, I have created a account and configured postfix to send through that. My emails are now working as the IP is not blocked by Microsoft. But I want this to be temporary, until my issue is fixed and reverted back.

@AmityWeb2021 How did you do that? perhaps that would be a solution until Microsoft wakes up from their deep slumber. Is there any documentation on how to setup a new smtp using a different IP?

I have had many responses from Microsoft saying they are escalating the issue, but nothing happens after that. very very disappointing.


Also I am sure that Linode IPs are all blocked because I have a server with Linode with no emails ever being sent from it for the past 2 years. I set up a totally new account and an unused brand new domain and tried to send to a Microsoft365 email account, it was blocked.


Linode should do something about this, as well as Microsoft. Otherwise I will have to just move to a different data center, perhaps DigitalOcean?


@bootahit depends on your current mail server... as I run my own server I have full control over it. So I can modify postfix's config files. The article how to do it is here I used to use Sendgrid some time ago, and its the same principle. In fact, I guess any 3rd party SMPT service can be used. It results in Postfix sending ALL email on the server through another SMTP account. My users still connect to their email accounts on our server, so they dont need to change any settings, but then our server uses another SMTP account to send them. That account would then have a different IP and is not blocked.

Great, will read and see if I can do the same. Doesn't sendgrid have a mon thly subsc ription? it would cost us a lot to run through third party. will try to setup our own if I can. thanks for sharing.

Yes they would mostly have a fee. I dont know of free ones, or if they were any good. This is why its temporary for me, I dont want to keep paying the additional cost. The cost will depend on how many emails you send through it per month. Its not a big cost even up to 100,000, but as its a business service I provide, so my customers pay me, I have no choice than to pay to get it working until Microsoft find someone who knows what they are doing.


If the cost is high, an alternative is create another server just like your mail server, if the cost for that is much less than sendgrid etc. and send through that. I think you can send through any server an email account to send through (I think, I have not tried it but dont see why not). Although it gets a bit advanced then because have done something with the return path in order to link the sending to the originating domain SPF record which is important to not get caught as spam. 

Linode support has kindly digested me this far and I am surprised to see how many people affected.


I have several servers affected in London and Frankfurt.


anyone with an email server in Linode US affected here?