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Server error: '550 5.7.1 Unable to relay'

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  • Server error: '550 5.7.1 Unable to relay'

    Hi all, I have a user that is connected to the organization exchange from home via POP3. When he try to send messages to external domain he get the respond - Server error: '550 5.7.1 Unable to relay' I searched the web and find that i need to go the smtp server and add my server to the relay restrictions but, that didn't help either. what can i do to solve this? Thanks for any help

  • #2
    Re: Server error: '550 5.7.1 Unable to relay'

    I just noted that when i try to configure the an additional account via pop on outlook, i get an error on test account settings when it try to send test email message but, the log on to incoming pop3 server is successfully. what could be the problem? it's probably my smtp server but my exchange users send email successfully.

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    • #3
      Re: Server error: '550 5.7.1 Unable to relay'

      I was able to connect via outlook with pop3 but i still get the
      Server error: '550 5.7.1 Unable to relay' when trying to send emails to external domains

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      • #4
        Re: Server error: '550 5.7.1 Unable to relay'

        Problem Solved.
        add receive connector, add the default gateway of my user's home connection to remote address, replace the smtp port to another number and opened the port in the firewall and it worked exchange is relaying

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        • #5
          Re: Server error: '550 5.7.1 Unable to relay'

          Well done, and thanks for posting back
          Tom Jones
          MCT, MCSE (2000:Security & 2003), MCSA:Security & Messaging, MCDBA, MCDST, MCITP(EA, EMA, SA, EDA, ES, CS), MCTS, MCP, Sec+
          PhD, MSc, FIAP, MIITT
          IT Trainer / Consultant
          Ossian Ltd
          Scotland

          ** Remember to give credit where credit is due and leave reputation points where appropriate **

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          • #6
            Re: Server error: '550 5.7.1 Unable to relay'

            What you did wasn't really necessary. Exchange has everything already in place.
            The most common mistake made when configuring an Exchange POP3 connection is enabling the option to use the same credentials as POP3 for outbound email, as this is how *nix based systems used by ISPs work.

            Not Exchange.

            You have to set it to use specific credentials and then enter the username and password in the format of domain\username for it to work.

            Although I don't recommend the use of POP3 anyway. If the end user has Outlook then use Outlook Anywhere. You can then backup the email and generally maintain control of it. With POP3, once the email has been extracted, it is out of your control.

            The solution you have implemented actually puts your server at risk of being abused. IP addresses can be spoofed and it is very easy to turn the server in to an open relay via that method. Use authentication to control relaying, preferably over TLS/SMTP over SSL, which will provide a secure connection - if you can't use Outlook Anywhere.

            Simon.
            --
            Simon Butler
            Exchange MVP

            Blog: http://blog.sembee.co.uk/
            More Exchange Content: http://exchange.sembee.info/
            Exchange Resources List: http://exbpa.com/
            In the UK? Hire me: http://www.sembee.co.uk/

            Sembee is a registered trademark, used here with permission.

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            • #7
              Re: Server error: '550 5.7.1 Unable to relay'

              Originally posted by Sembee View Post
              The solution you have implemented actually puts your server at risk of being abused. IP addresses can be spoofed and it is very easy to turn the server in to an open relay via that method. Use authentication to control relaying, preferably over TLS/SMTP over SSL, which will provide a secure connection - if you can't use Outlook Anywhere.
              Exactly.
              Use auth. Always.

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