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Resolve Exchange SMTP Error 550 5.7.1 Unable to Relay

SMTP Error 550 5.7.1 unable to relay

The emails are transferred from an email client to the server and vice versa using Port 25 with the help of Simple Mail Transfer Protocol. It is also responsible sending the data over the network. But, sometimes, it also creates some of the issues and displays the error message:”Fix Exchange SMTP Error 550 5.7.1 Unable to Relay“.

The Exchange Error 550 indicates that the user is not authenticated to the particular server. Therefore, it is unable to send the emails as well. One more reason behind the nonexistence of the particular Recipient’s policy of the specific domain in user’s department.

In most of the cases, Exchange Server Database Corruption is one of the most common causes that results in this error message. This blog will discuss this Exchange Server Error in detail and it will also help the users to perform Exchange Mailbox Recovery from corruption.

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Overview: SMTP Error 550 5.7.1 Unable to Relay

Sometimes, some cryptic error codes are given by the HTTP Protocol which restricts the users with email sending limitations. The important information about this persisting error is described by these error codes. The error codes consist of a three-digit code a particular attribute is defined by each of the three digits.

In such situations, users are required to fix SMTP error 550 by understanding the reason for its occurrence. The error message is clearly described in the following section:

The very first digit of the error code is used to describe that whether the Exchange Server accepts the command, encounters any action or it commences any appropriate action. Any connection or syntax errors that exist, are displayed by the subsequent codes.

If it prevents any unauthorized user from gaining access to the Exchange Server for gaining access then Exchange SMTP Error 550 5.7.1 unable to relay can be considered as a security specific error message.

The initial digit indicates that whether the server can accept the command. It is also designated using five different values:

  • The initial first value states that the command is accepted by the Server, as well as no action, has been taken and confirmation is awaited.
  • Second values describe that the task has been completed successfully.
  • The third value shows that the task has been understood by the server but the detailed information is needed to complete the task.
  • Fourth value states that a temporary failure has occurred; hence, it is necessary to re-execute the same command without any modifications to accomplish the task. Mail Servers use the temporary failures to keep the unauthorized senders away.
  • Fifth value shows that an error has been encountered.

The Second digit gives a detailed information with six different values. The description of all of them is given below:

  • Initial value states that a syntax error has occurred.
  • Second value shows an informational response.
  • Connection status is indicated by the third value.
  • Fourth and Fifth digit indicates unspecified errors.
  • Status of mail system as a whole and mail server, in particular, is indicated by the sixth one.

The Third digit in this cryptic error indicates a variety of the graduations of the mail transfer. A wide list of ESMTP Server response codes is being set-up by the Standard RFC 821 and following Extensions is displayed by it.

Symptoms of SMTP Error 550 5.7.1

Several Symptoms which confirm the occurrence of “Exchange SMTP Error 550 5.7.1 unable to relay”. Understanding the symptoms carefully will help to fix the SMTP error 550 before it may result in critical consequences. The symptoms of this error may include:

If the domain counts increase to some extent, then the following error message is displayed:

  • Email Delivery or Email Sending fails with the error code 5.7.1 or 5.7.3.
  • Exchange Server might send some commercial email messages and the remote domain will also send the information regarding spontaneous emails sent by the Exchange Server.

Factors for SMTP Error 550 5.7.1 Unable to Relay

When the user tries to deliver email messages outside the domain, then the error message appears. Various other reasons are also responsible for the occurrence of this error message:

  • The Outgoing Mail did not recognize the sender.
  • Several restrictions have been imposed on the Sender’s Domain through the Recipient’s policy defined by the Receiver Domain.
  • In the Exchange Database, Authentication may fail for the sender domain or the corruption may still exist.

Manual Approach to Fix Unable to Relay Error

The Manual technique to fix Exchange SMTP Error 550 5.7.1 unable to relay is discussed in the following Section:

  1. Firstly, users have to start the Exchange Server Manager.
  2. Navigate to Administrative Groups in the Exchange Manager.
  3. Choose Administrative Group Name → Choose ServerServer Name.
  4. Click on Protocols → Choose SMTP.
  5. Now, Select Properties by right-clicking on Default SMTP Virtual Server.
  6. Click Access Tab → Click Relay → Select Only the List Below.
  7. Now, choose the IP and the Domain that you want to relay.
  8. In the end to fix Exchange SMTP Error 550 5.7.1 unable to relay, check the box associated with “Allow all the systems to successfully authenticate to relay regardless of the list above”.
  9. Close all the opened Tabs. The SMTP Server will now enable you to send the emails.

Alternatively, In the application Event Log, you can check for all the existing Exchange Errors and also search corresponding resolution methods. Regular checking of the application event logs will help to observe the actual cause and time when the ‘Exchange SMTP Error 550 5.7.1 unable to relay’ error message is generated.

To resolve the Exchange unable to relay error, it is necessary to analyze the reason behind its cause. If this error occurs due to Exchange Server Corruption, then it can be resolved using Eseutil, which is an Exchange built-in tool provided by Microsoft.

The probability to resolve the error via Eseutil utility is directly related to the intensity of the corruption in the EDB files and the incorporated objects. In case of the severe corruption, it is always suggested to opt a professional third-party SysTools Exchange Recovery Utility.

Automated Approach to Resolve SMTP Error 550 5.7.1 Unable to Relay

Exchange Recovery Software is capable to recover corrupt offline/dismounted Exchange Databases file. The software not only recovers the data completely but is also capable to restore the recovered data into Live Exchange Server, Office 365 and various file formats.

This utiltity offer dual scanning mode that easily recover & repair EDB file from corruption. The quick scan remove minimal corrupted EDB file and for major corruption user can select advance scan option. It also recovers permanentrly deleted Exchange items and mailboxes from loaded Exchange database file.

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User can extrct Exchange EDB to PST, MSG, MBOX, EML, PDF, HTML file formats after recovery. Once, the files are saved in the desired file format, the data items can be accessed on independent Email clients such as Microsoft Outlook, Thunderbird and other web email clients.

The software automatically creates export report which stores success and fail count of export Exchange mailboxes data.

Key Features Of Automated Wizard

  1. Recover & Repair damged Exchange database file
  2. Perform Exchange 2016 mailbox recovery using scan mode option
  3. Keep metadata intact and preserve actual folder hierarchy
  4. Preview healthy EDB mailbox data items before conversion
  5. Backup Exchange mailbox to PST file and other file formats
  6. Selective export Exchange data by using date and category filter option
  7. Support all verions of Windows OS, Exchange Server, and Microsoft Outlook


It is necessary to have regular backups of the Exchange Server database which includes mails, contacts, etc. If the data gets damaged or corrupted, then these backups play a very important role. This blog describes SMTP Error 550 5.7.1 unable to relay and the techniques to resolve this error. Both the manual and automated approaches have their own benefits but the Automated techniques are more preferred by the users as it can recover the Exchange Server data in a reliable and efficient manner.

Shini is a freelancer technical blogger. An information seeker in arena of Technology, curious about sharing information through web among folks. Researched on various email clients problems & recovery solutions is currently willing to share all the information acquired with help of Blogs.