How To Fix ‘550 Permanent Failure For One Or More Recipients’

As a Managed VPS Service provider, we deliver technical help for customers round the clock. Since our support also includes helping customers with their email problems, so we solve many mail server related issues for our customers. One such issue our customers face is 550 permanent failure for one or more recipients. Today in this article we will see how we can debug and solve this issue. Recipient mail servers typically allow all the genuine emails, but due to various reason an email can be flagged as spam and you might receive 550 permanent failure for one or more recipients as an error, thus email being rejected by the recipient mail server.

There are two main reasons as to why you are receiving this error:


  1. Something is wrong with the receiving end.
  2. Something is wrong on the sending end.


If doing this is too much for you, you can sign up with us and let our experts do this for you. We offer 3 days free trial no credit card required start free with our managed vps now.

Other Similar Error Messages


Before diving into the solution, let see some other related error messages you might receive, such as:


  • 550 5.1.1 Sorry, no mailbox here by that name
  • 550 Requested action not taken: mailbox unavailable
  • 550 5.1.1 Is not a valid mailbox
  • 550 No such user here
  • 550 Invalid recipient
  • 550 Unknown address error ‘MAILBOX NOT FOUND’
  • 550  The email account that you tried to reach does not exist
  • 550 Recipient address rejected: User unknown in relay recipient table
  • 550  Address rejected
  • 554 delivery error: This user doesn’t have an account
  • 554 delivery error: Sorry your message to [email] cannot be delivered. This account has been disabled or discontinued
  • 550 permanent failure for one or more recipients
  • 550 User unknown


These messages usually mean something is wrong on the receiving end, but there is a high possibility that your email might be getting marked/flagged as spam (which is considered to be a problem from sending end)

Issues on the receiving end


Lets first discuss if there is an issue on the receiving end. Upon sending the email, you might have received following as a reply to your email:


This message was created automatically by mail delivery software.

A message that you sent could not be delivered to one or more of its recipients. 
This is a permanent error. The following address(es) failed:

[email protected]
host [168.xx.xx.xx]
SMTP error from remote mail server after end of data:
550 permanent failure for one or more recipients ([email protected]:blocked)


There are multiple reasons why receiving end blocked your email, for example:

1. Email address does not exist


Email address does not exist on the receiving end. In which case you might also get another similar error such as “550 #5.1.0 address rejected”. It is possible that you either mistyped the recipient email, or they have provided you with a wrong email address by mistake.


In this case, the solution is very simple, just make sure to use the right email. Contact your recipient through some other medium and ask them to provide you with a correct email address.


2. MX Record not configured correctly


MX record basically tells the world that for any domain such as mail server is You can find MX record for any domain using this tool. Enter the domain and click on MX, you will find an address such as Enter this ( ) address in the box again and click A record, and you will find an IP address of the email server for the domain.


However, it is the responsibility of recipient server administrator to setup correct MX records, because if they have configured wrong records, you are then sending emails to the wrong email server, which is why your email is being rejected. You can contact and let them know if you suspect that their MX record is not configured correctly.


3. False Positive on recipent email server


Since email spam is very common, many email servers use spam filters and implement various security mechanism to fight spam. Even though you were not sending any spam, it is possible that you got triggered on their spam filters and now further of your emails are being rejected.


You can use a telnet client to check if you can connect to their email server. Telnet using domain

telnet 25

Or first, you can find the IP address of email server using this tool and then directly telnet to the mail server IP.

telnet 25

If telnet reports any problem, then you are most probably blocked by recipient email server. We will now discuss various reasons on sender end, to see if something is actually wrong on the sending side. Later we will discuss how you can fix that.


If doing this is too much for you, you can sign up with us and let our experts do this for you. We offer 3 days free trial no credit card required start free with our managed vps now.

Issues on the sender end


Usually if there an issue on sending side it is either related to improper verification or your email content hit their spam filter. Following are the major issues that could happen on the sender side:


  1. Sending server IP blacklisted.
  2. Sender server issues.
    1. SPF Record not configured properly.
    2. Failed DKIM Verification.
    3. No DMARC Record.


1. Sending Server IP blacklisted 


Spam monitoring companies who keep an eye on servers which constantly send spam emails. Those companies maintain the list of servers involved in spam mailing. To fight against the spam, the majority of mail servers block the mail coming from a blacklisted mail server. So if you are facing 550 error you have to check whether your IP is listed on these blacklists.


You can check your IP against various block lists through this tool. If your IP is listed on any of the blacklists, there are very rare chances that your email will go through. If you are on a shared service, it is possible that someone else is sending spam emails due to which your IP got blacked listed. However, if you are on a VPS, either your VPS got hacked and being used to send spam emails or someone sent spam emails using this IP before you.


Interesting similar read -> Email Blacklist Removal


Bottom line:


Spam is a very serious problem. Purpose of blacklisting is to reduce the spam in the mailbox of the customer.


2. Sender Server issues


Let’s evaluate some error messages you see when your mail server is misconfigured or your email server is a source of the spam mailing and sees how ‘550 permanent failure for one or more recipients’  occurred by sender server issues?


So if you want your emails not to be triggered as spam make sure that your SPF record is configured correctly or not missing and your RDNS record is configured in the right way. If your RDNS is not set you have to contact your VPS provider and request them to configure it.


Verify SPF, DKIM, DMARC, and RDNS for your Sending Domain


These days a lot of spamming is going on. Many people use email spam to do credit card and bank fraud, the question is how they do it? Most of the time people impersonate to be the owner of the domain and send email through a domain they don’t own. For example, they can configure their email software to send email from hello [a] cyberhosting [dot] org even if they don’t own the domain.


However now there are various ways to counter this issue, there are certain TXT DNS records (SPF, DKIM, DMARC) that you can publish. This way receiving end can make sure that your email server is authorized to send an email for We will discuss those records one by one.


SPF or Sender Policy Framework (What is an SPF Record)


SPF is a simple DNS TXT record. It basically lists IP Addresses of the server(s) authorized to send emails on behalf of a said domain. An example of SPF TXT record is


v=spf1 a mx ip4: ~all


In this example, you are allowing IP Address to send an email on behalf of your domain, so if someone tries to impersonate your domain and this record does not exist, their emails won’t deliver and they may face with 550 Permanent Failure For One Or More Recipients error. Thus this record is very important if you want to make sure that emails are delivered properly. Many mail server uses a security feature called SPF (Security Policy Farmwork) to ensure the authenticity of the mail sender and when you send emails from your mails server that are not mentioned in SPF record of your domain, the recipient mail server considers it as a fraud and won’t allow delivering the email.


DKIM or Domain Keys Identified Mail (What is an SPF Record)


DKIM is little tricky, however, it is also published as a DNS TXT record for the domain. It is a mechanism that allows the receiving end to check that an email was actually sent and authorized by the owner of the domain, thus another level of protection on top of SPF. If receiving end can make sure that email is signed with a valid DKIM signature, it guarantees that parts of emails have not tampered and the original message is received.


So it is highly recommended to use DKIM record along with SPF to improve email deliverability and at the same time prevent any spam that can originate from your domain.


RDNS Record


RDNS is reverse DNS record which means IP address to domain mapping, usually, DNS is about Domain to IP Address mapping but RDNS is reverse of it. RDNS record is very important in email delivery. This record is set by the owner of the IP, in this case, your cloud provider or if you are our customer we can set this record for you. We will also help you to set all the remaining records too and make sure your server is ready to deliver emails properly.


Verify if above mention records are set


Let’s check if our domain is vulnerable or not,  or if there is any misconfiguration. Go to this (G Suite Toolbox  ) enter your domain name and get all the TXT record for your domain. Look for SPF record, shows like this v=spf1. Then in TXT look for DMARC 1 which begins with v=DMARC1 at the subdomain _dmarc (


If the SPF-record ends with “-all” that is enough. If it instead ends with “+all” or “~all” the DMARC-record needs to have “p=reject” or “p=quarantine“. In any other case, it would be considered insufficient.


The SPF-record should exist on all subdomains as well, while DMARC is only on the main domain. If you want to set SPF, DKIM, and DMARC policy in CyberPanel, please refer to this link -> 


In short make sure you have following records set, so the receiving end can make sure that you are the actual owner of the domain email is being sent from, otherwise, the receiving end may think that you are using someone else domain to send spam email.


  1. Valid RDNS record. (If you are our customer, you can contact us to have it set up).
  2. Proper SPF record.
  3. Sign your messages with DKIM.
  4. Have a DMARC policy.


If doing this is too much for you, you can sign up with us and let our experts do this for you. We offer 3 days free trial no credit card required start free with our managed vps now.

Secure SSH

How to Secure SSH 


Securing SSH is one of the most important task of a system administrator. CyberPanel allows you to change SSH port, disable root login and save your SSH keys.


Basic SSH Secure 


Go to Security > Secure SSH



On this page you can control two settings:


  1. Change Default SSH Port.
  2. Allow/Disallow Root Login.


SSH Keys


To add your SSH keys, you first need to generate a pair of a public/private key.

On your local machine


  1. cd ~/.ssh
  2. ssh-keygen -t rsa -f cyberpanel -C root


This will generate two files cyberpanel and

You need to copy contents of 

Go to SSH key section click on “Add key” and paste the content in the following box:




Now on your local machine you can login without needing a root password using:

  1. ssh -i ~/.ssh/ [email protected]<IP Address>





Add Firewall Rule


CyberPanel follows deny all rules except for the ports opened by default, you can see default opened ports at: Security > Firewall



  1. Give this rule a name.
  2. Select protocol from dropdown either tcp or udp.
  3. Enter which port to open for specified protocol.
  4. Click ‘ADD’.

This will add rule and reload firewall.


Delete Firewall Rule


Just click on the cross button on right side of the rule, this will delete the rule and reload firewall.

Managing Users

How it works


By default there are three kinds of ACLs created upon fresh installation:

  1. admin
  2. reseller
  3. user

These three ACLs cannot be deleted or modified, however, you can create more custom ACLs.

Note: You can Manage CyberPanel in our Cloud Platform with extra features in it which are only available in CyberHosting Platform.


You can create new ACL by setting the following credentials to your new users:



Custom ACLs


For Custom ACLs click on “Manage CyberPanel” Button as showing in picture below:



then Click on “Create New ACL







Switch Sites Between Pure OpenLiteSpeed and Apache + OpenLiteSpeed

In our privious documented we’ve discussed how you can create a website that use Apache as back end server. You can read about it here. If you want to learn more about this feature you can do that here. But let say if you have initially created website without using Apache as back end server, what can be done then? Answer is very simple, you can use Apache Manager to switch to Apache plus OpenLiteSpeed or vise versa at any point.

Switch to Apache + OpenLiteSpeed


Nagivate to Services -> Services -> Click Manage on Related Service -> Click Manage CyberPanel


There you will see list of websites, click on Launch Icon for the website you want to perform switch on. Then you will land on following page:



From the left menu under Apache Manager Click Switch. You will then land on page where you can switch to Apache + OpenLiteSpeed or pure OpenLiteSpeed (if site is on Apache + OpenLiteSpeed) with one click.



Here just select the desired PHP Version and click the switch button, you can see that button says Switch to pure OpenLiteSpeed as this site was originally created with Apache as back end.

How to create Website that use OpenLiteSpeed + Apache

We’ve discussed about Apache being used pararrel with OpenLiteSpeed in our privious doucment here. In the privious document we’ve discussed about what it is and its benefits. In this document we will learn how we can create a website that use OpenLiteSpeed + Apache.

Before moving forward you need to order a VPS through our platform and make sure it is already up and running, you can follow our order guide for more details regarding this.

Creating Website using Apache as Back end




Go to Services -> Services -> Click Manage, you will see a page where you can do basic management of your managed CyberPanel VPS, it will look something like:




Once there click Manage CyberPanel, it will take you the to page where you can manage various aspects of your server including creating a website. From top right corner click Create Website, and you will land on a page that will look like:



Here you can create website, fill all the details and make sure you check Apache as Back end. If this is your first website where you selected Apache it will then take some time to install Apache and PHP-FPM. Stay calm while the sites get created.


Please note that if your server have LiteSpeed Enterprise checking Apache as Back end will not make any difference because LiteSpeed Enterprise already offer all the features that Apache has to offer.



Automatic Support System

How To Create a Support Ticket


To create a support ticket client must log in to CyberHosting  Cloud Platform. In CyberHosting Cloud Platform go to support section ‘Create Ticket‘ is to be clicked. Then you see ticket support form, where you need to click on ‘Department‘ and In the menu the best issue which describes the technical issue is to be selected. Next is very import ‘Subject‘ here you have to enter the subject of issue you having. and in the last box you have to describe the issue you are facing.


Support Ticket Form 



By clicking on ‘Create Ticket‘ you will successfully submit the ticket.


List of Tickets 


You can see the submitted ticket by going to ‘List of Tickets‘ under support section in your CyberHosting Cloud Platform. Every ticket has its own unique ticket id and client will be notified if Support Staff reply your ticket, you will get notified on your email address.


CyberHosting Cloud Platform support stuff active 24/7 you contact them any time.


Support tickets are extremely helpful in the circuit of Web Host Managers and is used by many big business houses nowadays.


OpenLiteSpeed + Apache on CyberHosting Platform

At CyberHosting we use CyberPanel. We have a product line called CyberPanel VPS, this product line make use of OpenLiteSpeed web server. OpenLiteSpeed is fast and Event driven web server and have intelligent cache module that can help you achieve much better results when compared to NGINX or Apache. You can read this post as to why people start to use OpenLiteSpeed server.


However OpenLiteSpeed does not fully support .htaccess rules, also there is no support for custom php.ini files in OpenLiteSpeed.


Thus at CyberHosting we developed a solution where you can use Apache behind OpenLiteSpeed.

How that works?


On front end still you use OpenLiteSpeed, on backend Apache is configured. Thus you can still benefit from OpenLiteSpeed cache module and get similar speed benefits plus full support of .htaccess rules and custom php.ini files.


You can set inidividual websites on your server to either use OpenLiteSpeed purely or use a mix of Apache + OpenLiteSpeed.


You can also convert later between OpenLiteSpeed and Apache setup at any time, in our later tutorials we will learn how we can make use of this feature.


Learn How to create Website that use OpenLiteSpeed + Apache

Billing System

Billing System in Our Platform 


CyberHosting Cloud Platform equipped with a powerful and flexible billing system. You just need to go to billing section of client area and add your funds for hosting services. There are two ways to add funds in CyberHosting Hosting Cloud Platform:


1. Add Funds via Credit Card



2. Add funds via PayPal



You have to Add funds after 3 days of free trail period!


After Adding funds you can see the amount is successfully added to your account, on the same page you can see your transaction history at the bottom.



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