proxyaddresses same as external Mail URL - ERROR 550 5.1.10 RRS feed

  • General discussion

  • Hello everybody

    We migrated from Exchange to 0365. The old domain was, and it's still available in the proxyaddresses attribute. It's temporary used for receiving mails via popcon.

    If a user sent with the new domain to user(at),  which is external, I received the error 550 5.1.10.  Mailbox cannot be found on exchange or O365. That's logical because the mailbox is an external mailbox. But is also added as accepted domain.

    Can you help me? Is there any solution.

    If you need some more information, let me know.

    Best regards 
    Friday, November 25, 2022 11:28 AM

All replies

  • Tips to fix a 550 error-
    Check for email address typos. 
    Check whether the email IP is blacklisted. 
    Try sending the email after some time. 
    Try changing your outgoing mail port.
    Check whether IP filtering is enabled.
    Enable SMTP authentication. 
    Troubleshoot the SSL method. 
    Contact your ISP.


    Rachel Gomez

    Monday, December 12, 2022 5:13 AM
  • Here are some possible causes for email error 550:

    Your email address has been compromised and so is blocked by the recipient's mail server.
    The recipient's email address doesn't exist.
    The recipient's email address is temporarily unavailable or suspended.
    The recipient's hosting server is temporarily unavailable.
    Your domain name is invalid or blocked.
    Your internet gateway has a firewall or a filtering feature which mistakenly identified your email as spam and blocked it.
    Your email is mistakenly identified as spam by the recipient's mail server.
    You are using your email client from a different IP address.
    The recipient's mail server failed to identify your email address.

    Try these steps:

    1. Check for email address typos
    Email Error 550 can occur due to typos in an email address. Make sure the email address you entered is correct, and there are no extra spaces or misspellings. There are also chances for the recipient to have given you the wrong email address. Confirm with them as well.

    Along with that, check whether your email address is entered correctly and your email has contents in it. Some mail servers will reject an email having no content in it.

    2. Check whether the email IP is blacklisted
    If your email IP is blacklisted in a DNS blacklist, most of your emails won't reach the recipient and will bounce instead.

    3. Try sending the email after some time
    There are chances that the recipient's server is temporarily down due to several reasons. Inform the recipient that the server may be down, and ask for an alternative email address or wait for a few minutes or hours till you try again.

    4. Try changing your outgoing mail port
    If your email application uses port 25 as an outgoing mail port, there are chances for servers to block the email as spammers use port 25 often to send spam messages. Try changing your port to 26, 465, 587 or 2525. 

    Note: If you are using a firewall, you will have to verify the change in port to allow traffic to pass.

    5. Check whether IP filtering is enabled
    Your SMTP server may be set up to authorise users from only a specified set of IP addresses. If that's the case, you won't be able to send messages from other locations. You can quickly resolve this by contacting the admin of your mail server.

    6. Enable SMTP authentication
    In most email applications, the SMTP authentication is automatically configured. In case, the application fails to configure it; you won't be able to send emails. Luckily, you can configure SMTP manually.

    7. Troubleshoot the SSL method
    As discussed, a majority of email clients use an auto detect feature to set up SMTP. While setting up SMTP manually, there will be several combinations of SSL available, including:

    During manual setup, you will need to verify the SSL method used by the SMTP server and configure the email client subsequently.

    8. Contact your ISP
    If the above solutions fail to resolve your issue, then it's advised to contact your Internet Service Provider for assistance. There are chances that your ISP's filtering system might be blocking your email.

    I would appreciate a vote :-)

    • Edited by Sahin, Erkan Monday, January 30, 2023 11:27 PM vote
    Monday, January 30, 2023 11:27 PM
  • Hello zNici, 

    Please make also sure that "" is added as the primary proxy in AD.

    you can do this by adding SMTP in capital letters for example 

    and the old email you can add as an alias like 

    Hope this helps

    Monday, February 6, 2023 10:13 PM