How to fix '550 permanent failure for one or more recipients' and similar errors

550 error

As a company providing technical support for clients servers and infrastructures - we often face with situations when our customers have 550 permanent failure for one or more recipients error or any kind of another 550 error. Such errors may occur with emails in Exchange and Postfix servers.

Reasons of getting and different kinds of 550 error message

Example of messages associated with this error:

550 permanent failure for one or more recipients

550 User unknown

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 #5.1.0 Unknown address error ‘MAILBOX NOT FOUND’

550 5.1.1 The email account that you tried to reach does not exist

550 5.1.1 Recipient address rejected: User unknown in relay recipient table

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 #5.1.0 Address rejected

Of course, there are other similar error messages that you might see we've just focused on the most common ones. There are two main reasons for getting such as "550 permanent failure for one or more recipients" message - the issue may be in the sender or recipient server.

Recipient server issues:

If you'll see a message similar to any of these, you must contact the recipient by other means (telephone, Facebook or any other form of contact) asking the recipient to contact the email server’s hosting company or the network administrator of the company (in the case of corporate emails) to fix the problem. Ideally, you should forward the error message to the recipient using a working email address, so he or she can forward to the person in charge of the email server’s configuration.

Sometimes you may send an email to the wrong email.

In 80% of cases "550 #5.1.0 address rejected" error is caused by sending mail to the wrong address. Pretty typical mistake, that can cause such errors. Emails may also be bounced if you are sending an email to a non-existing address, or an address that is no longer in use on the recipient server.
If the problem is in validity of the recipient address - you will get "550 5.1.1: Recipient address rejected".
To solve this you just need to check if the address you are sending an email is existent and typed correctly.

Misconfigured MX record on the recipient domain

The other reason for bounced emails may be related to the misconfiguration of the recipient's MX record. If the address that you are sending a message is resolving wrongly - the recipient's server will be unable to process an email account and the email will bounce.
To solve this you should check the MX records of the recipient domain by the following command:

dig MX

If you notice any misconfiguration in MX records - you should contact recipients server support with a request to solve the issue. Note that this error is on the recipient's side, not yours!

Recipients mail server misconfiguration

The majority of the mail servers are tuned with security measures and custom security solutions. Such security configurations like firewalls and spam filters are usually used to block undesirable emails from reaching the server and spam filtering.
First of all, you need to understand whether the recipient's firewall is blocking your server or not:

telnet 25

If a firewall or spam filter are bouncing your email - verify the recipient's filters and blacklists.

Sender server issues:

Let’s now review a few error messages so you can see if there is something wrong with your email server configuration or if your email server is flagged as a source of spam. The root of such as "550 #5.1.0 address rejected" errors may be caused by sender server issues.

You are sending spam

The majority of mail servers (such as Postfix and Exchange) have an option to bounce emails from non-verifiable emails. Also, most mail servers check blacklists before pushing the mail to the recipient, and if your mail server is blacklisted - your email will be bounced.
To make sure your emails are not considered spam - check if your SPF records exist and RDNS is configured accurately:

host your_IP_address

Also, you need to make sure that your IP address is not blacklisted.

Your email account is hacked

Hackers are not sleeping nowadays, and you can't be 100% sure that your account is secure and protected. If you notice any emails that you didn't send or some spam that is been sent from your account without your involvement - check the logs and ensure you don't have any script for mass spam mailing.
The first thing you need to do is check if there are any spamming scripts. If there are no such - change the password, use some kind of strong random password generator and restrict access to your mail only for several IPs.

Sender server misconfiguration

Even such simple issues in the configuration like the configuration of the recipient domain as a local domain in the sender server may cause email bouncing. Yeah, that's pretty weird, but still, a reason to double-check your mail server configuration :)

Let's summarize when you can get '550 permanent failure for one or more recipients:

There may be many reasons that cause "550 permanent failure for one or more recipients" error, which can both be related to the recipient side and the sender side. You need to check the valiance of the recipient's email and if you typed it correctly. If this will be not enough - ITsyndicate will be happy to help you.