Why did I get this and how to correct ?  Reason 550 - relay email not allowed

Posted on 2006-05-01
Last Modified: 2012-05-05

One of our users received the following response to an email he sent:

The following addresses had permanent fatal errors ----- <>
    (reason: 550  Relaying mail to is not allowed. If you are using an e-mail client (e.g., Outlook Expr...

 ----- Transcript of session follows ----- ... while talking to
>>> DATA
<<< 550  Relaying mail to is not allowed. If you are using an e-mail client (e.g., Outlook Express, Netscape Messenger, etc.) to send or receive e-mail from your current location, you may need to change the Incoming and Outgoing server settings on your e-mail client. Your local Network Administrator can provide the proper server settings for your e-mail client. For more information, please visit
550 5.1.1 <>... User unknown <<< 503 No recipients specified

The user has successfully sent emails to this address before.  What is the cause of this and what can be done to fix?  Please be specific and descriptive with your answers.  Thanks for your time.


Question by:dweb937
    LVL 18

    Expert Comment

    SMTP servers are the real workhorses of e-mail as they are the computers sending all those millions of messages every day. But as all e-mail users know, many of those messages are infected with viral attachments, or are spam (unsolicited commercial e-mail), or are scams (please let me use your bank account to get millions of dollars out of Nigeria). To prevent spammers and malicious users from sending mail via their server, most ISPs have placed restrictions on who is allowed to access their SMTP server. For most people this is not an issue, since most people use only one ISP and one e-mail account hosted by that ISP. If you sometimes use a second ISP though, or if you use an e-mail address other than the one provided by your ISP, the SMTP server may not recognize you as an authorized user and so will refuse to send your messages. Instead the server will issue an error message which Outlook Express will display. The exact text varies but will usually include the error code "550 - Relaying not allowed."

    ISPs use several methods for detecting authorized users. Some configure their SMTP servers to accept mail only from computers that are connected to the Internet using the ISP's modem bank, cable, or DSL line. Some also use the sender's e-mail address and reject all mail sent from addresses not hosted by the ISP itself. Some allow you to authorize with the SMTP server using the same logon name and password used to access the POP3 server. Some use a method known as "POP before SMTP" by which you must first access the POP3 server using your logon name and password, which then gives you permission to access the SMTP server for some minutes. If you encounter relaying problems, you will have to ask your ISP's helpdesk which method they use, and get their help in configuring your Outlook Express accounts.


    Author Comment

    Thanks for your response.  I'm not sure how this applies to us?  We're using Windows Exchange and MS Outlook for email with our domain.  Our email is not being hosted by our ISP which is AT&T.

    In your second paragraph, it sounds like it's the recipient's ISP that is not accepting the email - I'm confused?

    LVL 104

    Accepted Solution

    This is your problem: User unknown
    The rest of the message is just fud.

    A DNS Report shows exactly what the problem is.

    They have multiple MX records in their domain. Most of them are from MXLOGIC, but there is one that appears to be an ISP. That one server is generating the message that you are seeing above. For some reason your server is trying to use that one server for delivery of email.
    I suspect that the server is not valid for that domain.

    The solution is for the remote side to remove that server from their MX records, particularly as they using MXLOGIC.


    Author Comment

    This is all greek to me but I see what you're saying when I read through the report.  That's a nifty tool.  Simon - thanks for your help!  

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