How to fix email error ‘501 5.1.7 invalid address’ in Exchange servers

How to fix email error ‘501 5.1.7 invalid address’ in Exchange servers

A commonly noted error in Microsoft Exchange 2007 server is when the emails from certain 3rd party applications or scripts fail to deliver.

The mails get rejected, giving this error message in the logs:

SMTP MAIL command failed Error (501) 5.1.7 Invalid address

Today, we’ll see what this error means and how to fix it in Exchange server.

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What is error ‘501 5.1.7 invalid address’?

As we all know, a valid email address has the format – But in many email applications, people give the alias names in mail address fields – say, just ‘username’.

In older versions of Exchange, the default domain name gets appended automatically to these alias entries given in ‘MAIL FROM:’ or ‘RCPT TO:’ fields of email applications.

So, even if aliases are used, they get automatically converted to fully qualified email addresses by the Exchange server. But from Exchange 2007 onwards, this feature is absent.

So, when mail users try to send a mail with just an alias name, Exchange 2007 DOES NOT replace it with the full mail address, and it results in  ‘501 5.1.7 invalid address’ error.

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