SMTP stands for Simple Mail Transfer Protocol that works to send emails between the server and its email clients. It works the same in the Exchange Server and is used for communication between the Exchange Server and its client. However, sometimes, you will face some issues like 550 5.7.1 error code displaying “Unable to relay” while trying to send emails through SMTP. Let us find out what is Exchange SMTP error 550 5.7.1 and then ways to fix this to get back emails accessibility hindered before.

What is Error SMTP error 550 5.7.1?

The SMTP error 550 5.7.1 occurs in In Exchange 2016, 2013, 2010, or 2007 versions while users trying to send emails. If Exchange finds that any unauthorized user is accessing the Exchange Server, then it will display SMTP error 550 5.7.1 with the error message “Unable to relay.”

This error can happen to any user and can block emails from being sent. This error consists of three-digit codes, and each digit has a meaning.

What are the causes of SMTP error 550 5.7.1?

There are some factors that are responsible for this error like:

  • There is an unknown sender, or the Outgoing Mail Server does not recognize the sender.
  • Sender domain fails to be authenticated
  • The recipient policy of the receiver domain blocks emails from the sender domain.

How to fix 550 5.7.1 error unable to relay in Exchange Server

  1. Launch Exchange Server Manager and move to Administrative Groups.
  2. Select Administrative Group Name then choose Server>Server Name.
  3. Now click on Protocols and Select SMTP.
  4. Right-click on Default SMTP Virtual Server and select Properties
  5. In Access tab, click on Relay>only the list below
  6. Now check the checkbox “Allow all systems to successfully authenticate to relay regardless of the list above” and close.

Now you can send messages as normal.

What to do if you are not able to send messages because of EDB corruption?

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Exchange SMTP error blocks sending and receiving emails from server to client due to unknown sender, incorrect authentication, or recipient policy based on which a manual solution via Exchange Server Manager is explained. Inability to access Exchange data can also occur due to corruption in the database file and so, a trusted professional Exchange Recovery tool is suggested for the Exchange users.