Solved: Exchange SMTP Error 550 5.7.1 Unable To Relay

Exchange server uses Simple Mail Transfer Protocol (SMTP) to send emails from an email client to the server and vice versa. It is responsible for sending data over the network. In Exchange, after enabling the IMAP or POP3, you must configure the authenticated SMTP settings for users so that they can send emails.

Sometimes, the email delivery may fail and the following message may get relayed back to the server - an SMTP error code 550 5.7.1,

"The SMTP mail system returned the following error: (0x8004020F): The server rejected one or more of the recipient addresses. The server response was 550 5.7.1 Unable to relay"

In a nutshell, this message is a non-delivery report (NDR) or delivery status notification (DSN) of emails. The error 550 5.7.1 generally implies that the user is not authorized, and therefore, fails to send emails. As a result, the message is relayed back to the server.

What is SMTP Error 550 5.7.1 Unable to Relay?

The error ‘550 5.7.1 Unable to relay’ is a cryptic error code by HTTP protocol, which restricts users from sending emails. The error codes describe important information about the persisting problem. It usually consists of three digits where each digit defines a particular attribute. In such a situation, you need to fix the SMTP error 550 by understanding the meaning and reason for the occurrence. The description of the error 550 Unable to relay a message is as follows,

• The first digit describes whether the Exchange server accepts the command, encounters an error, or commences appropriate action.
• The subsequent digits display if any connection or syntax error exists. It can be considered as a security-specific error message if it prevents unauthorized users from gaining access to the Exchange server for relaying emails. 

What Factors are Responsible for SMTP Error 550 5.7.1 'Unable to Relay'?

There could be various reasons responsible for the occurrence of Exchange SMTP error 550 Unable to relay error. These are:

• Authentication failure/don’t have permission to send messages to the recipient
• The sender address is not recognized by the Outgoing Mail Server
• Exchange database corruption
• The Recipient Policy of the recipient domain blocks the emails from the sender domain
• Email routed to the wrong server
• Sending an email to a large distribution group

Most commonly, the reason could be database corruption or the nonexistence of a specific Recipient's policy for the particular domain in the user's department in the Exchange server database(s) that results in this error message.  

How to Fix Exchange SMTP Error 550 5.7.1 'Unable to Relay'?

Below we have provided a few manual solutions to fix Exchange Error 550 5.7.1. However, you may require considerable technical expertise to execute the steps. Hence, good know-how of the Exchange server processes is essential. You also need administrator access and permissions to execute the commands and steps discussed below.

Method 1: Check Event Logs

Check for all existing Exchange server errors in the application event log and search for corresponding resolution methods online. Checking the application event logs will help you analyze the actual cause and time when the 'Exchange SMTP Error 550 5.7.1 unable to relay' error message is generated. 

Method 2: Contact Recipient or Recipient’s Email Admin

As mentioned earlier, if the sender’s address is not recognized by the Outgoing Mail Server, the email delivery may fail. In such a case, you may contact the recipient or recipient’s email admin to fix the problem from their end. Tell the admin or the recipient about the email delivery problem and ask them to reconfigure the recipient’s mailbox. This may help you stop the SMTP error 550.

Method 3: Use Exchange Server Manager

You can use the Exchange Server Manager to fix the failed email delivery issue and the Exchange SMTP error 550 5.7.1 Unable to relay. The steps are as follows:

• Start Exchange Server Manager
• Go to Administrative Groups in the Exchange Server Manager
• SelectAdministrative Group Name, select Server, and then the Server Name
• Next, click on Protocols and select SMTP
• Then right-click Default SMTP Virtual Server to select Properties
• Click on the Access tab and then click on Relay to select only the list below
• Next, select the IP that you want to relay and the domain
• Finally, check the box associated with "Allow all computers which successfully authenticate to relay regardless of the list above"
• Close all opened tabs. The SMTP Server now enables you to send emails

Method 4: Use EseUtil

Sometimes, the SMTP error 550 5.7.1 may also occur due to a problem with the Exchange database file (EDB). Common factors, such as virus or malware intrusion, power failure, force shutdown, incompatible antivirus software, or server crash, may cause database corruption that can lead to the ‘Exchange SMTP Error 550 Unable to Relay’ error. To fix database corruption, you can use the EseUtil, an Exchange built-in utility offered by Microsoft. You can also use EseUtil, which is located at C:\Program Files\Microsoft\Exchange Server\Vxx\Bin, to check database integrity, defragment the database, and reduce the database size.

Following are some EseUtil commands that you can use to perform various operations on the Exchange database.

• Defragment Database

ESEUTIL /D

• Check Database Integrity

ESEUTIL /g < path to database file>

• Perform Soft Recovery

ESEUTL /P

In Exchange 2010 and earlier versions, you need to use the Isinteg as EseUtil is available in Exchange 2010 SP1 and later versions only.

Isinteg –s

• Perform Hard Recovery (May cause Data Loss)

ESEUTIL /C

TIP: Always dismount the database and create a backup copy of the database before performing any operation on the Exchange database file.

Method 5: Use an Exchange Recovery Software

The probabilities to resolve the error via EseUtil is based on the intensity of corruption in the EDB files and incorporated objects. Plus, it may cause permanent data loss, if hard recovery is performed. Thus, in case of severe corruption and to avoid data loss, it is always better to deploy a professional Exchange recovery software, such as Stellar Repair for Exchange.

The Exchange recovery software repairs corrupt and damaged Exchange database files, extract the mailboxes, and saves them as PST without any data loss. You may also import the extracted mailboxes and mailbox items to the live Exchange server directly by using the software. Plus, it also helps Exchange admins to recover and restore deleted mailboxes from Exchange 2019, 2016, 2013, 2010, 2007, 2003, 2002, 2000, and Exchange 5.5 database files in a few clicks.

Final Thoughts

The 550 5.7.1 Unable to relay SMTP error can be resolved by following the manual methods discussed in this guide. However, these methods work only if the reason for SMTP 5.7.1 error is due to authentication, recipient policy, and permission related problems. These methods won’t work if the problem is caused due to integrity issues with the Exchange database file.

In such cases, you may use EseUtil to repair the database via soft or hard repair commands. But EseUtil may cause data loss and fail to repair the database if the corruption is severe. To avoid data loss and restore mailboxes from a severely corrupt or damaged database, you can use an advanced Exchange recovery software, such as Stellar Repair for Exchange. This can help you quickly fix the problem with the Exchange database and avoid the Exchange SMTP error 550 5.7.1 Unable to relay error message.