Solved: Exchange SMTP Error 550 5.7.1 Unable To Relay

Updated on July 3, 2019

Simple Mail Transfer Protocol (SMTP) is used to transfer emails from an email client to the Server and vice versa using Port 25. It is responsible for sending data over the network, however sometimes, it create issues thus displaying the error message “Fix Exchange SMTP Error 550 5.7.1 unable to relay.”

Error 550 implies that the user is not authenticated to the server, and therefore, it fails to send emails. Another reason could be the nonexistence of specific Recipient’s policy for the particular domain in the user’s department. In majority of cases, corruption in the Exchange Server database(s) is the most common reason that results in this error message. Let’s understand this error message in detail. 

About the SMTP Error Code

Sometimes HTTP protocol returns cryptic error codes and restricts users with email sending limitations. These codes describe important information about the persisting error. It consists of a three-digit code 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 occurrence. The description of the error message is as follows:

The Initial digit describes whether the Exchange Server accepts the command, encounters error, or commences appropriate action. The subsequent codes displays 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. 

The first digit that indicates if the Server can accept the command and handle it is designated by five different values:

  • First value indicates that the command is accepted by Server, however, no action has been taken and a confirmation message is awaited
  • Second value indicates that the task has been successfully completed
  • Third value indicates that the server understands the task but a detailed information is required to accomplish the task
  • Fourth value indicates that a temporary failure occurred: hence, re-execute the command without any modifications to complete it. However, temporary failures can be used by mail servers for keeping unauthorized senders away
  • Fifth value indicates that the Exchange Server has encountered an error

The second digit provides a detailed information using six different values. Descriptions associated with all the six values are described below:

  • First value indicates that some type of syntax error has been occurred
  • Second value indicates informational response
  • Third value indicates the connection status
  • Fourth and Fifth value are unspecified reasons
  • Sixth value indicates status of mail system as a whole and mail Server in particular

The third digit in the cryptic error code specifies a variety of graduations of the status of mail transfer. It displays a wide list of ESMTP Server response codes being set-up by standard RFC 821 and following extensions.

Identify Symptoms that Indicates SMTP Error 550

There are several symptoms that confirm the occurrence of ‘Exchange SMTP Error 550 5.7.1 unable to relay.’ Analyzing the symptoms carefully may help fix SMTP error 550 before it leads to critical consequences. The symptoms include:

  • Error message may appear if the domain counts increase to some extent
  • Email sending or email delivery fails with error code 5.7.1, 5.0.0 or 5.7.3
  • Exchange Server may send commercial email messages and the remote domain will send information regarding the unsolicited commercial emails sent by your Exchange computer

What Factors are Responsible for ‘Unable to Relay’ Error

The error message appears when the user tries to deliver email messages outside the domain. Several other reasons are also responsible for the occurrence of this error message -

  • The sender is not recognized by the outgoing mail server
  • The Recipient’s policy defined by receiver domain has imposed several restrictions on the Sender’s domain
  • Authentication fails for the sender domain or Corruption may exist in the Exchange Database

How to Fix Exchange ‘Unable to Relay’ Error

The manual resolution to fix Exchange Error 550 5.7.1 is provided herein. Here, you may require considerable technical expertise to execute the steps. Hence, a good know-how of the Exchange Server processes is essential. Follow the steps below -

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

Alternatively, you can 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 ‘Exchange SMTP Error 550 5.7.1 unable to relay’ error message is generated. 

To fix Exchange Error 550 5.7.1, it is important to understand the reason behind the cause. If the error is due to Exchange corruption, it can be rectified using Eseutil, an Exchange built-in utility offered by Microsoft. The probabilities to resolve the error via Eseutil is based on the intensity of corruption in the EDB files and incorporated objects. In case of severer corruption, it is always better to deploy a professional third-party Stellar Mailbox Exchange Recovery software. 

The Way Forward: Stellar Repair for Exchange

This software recovers corrupt Exchange databases. Other than complete recovery of data, the tool restores the recovered data in multiple file formats. After saving data in the desired file format, the mailbox items can be accessed on independent email clients such as MS Outlook, Windows Live Mail, Thunderbird, Apple Mail, and other desktop and web email clients. It supports Exchange 2019, 2016, 2013, 2010, 2007, 2003, 2002, 2000 and Exchange 5.5 editions. It also provides different connection options that include (i) connection to single mailbox; and (ii) connection to all the mailboxes on the Server. Therefore, Stellar Repair for Exchange is the ideal solution for fixing Exchange SMTP Error 550 5.7.1.


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