Mail relay problem using POP3 service

Posted on 2005-04-26
Last Modified: 2011-09-20
I have a similar question to another already asked in this forum.

I have several users on my domain that when outside the office can not send to an outside company email address.  The difference is that I do not have a SMTP server set up - my users are using a POP3 mail service from an ISP-type of provider.

However, since at work they access the internet thru a Small Business server, and at home they access directly, they get the following error:

"Your message did not reach some or all of the intended recipients.

      Subject:      RE: Email problem
      Sent:      18/04/2005 12:01 PM

The following recipient(s) could not be reached:

      '' on 18/04/2005 12:01 PM
            550 relaying mail to is not allowed"

Is there any way to address this problem ?
Question by:pbissegger
    LVL 3

    Accepted Solution

    It's not entirely clear to me from what you're saying, but I suppose those users you're talking about are running around with notebooks under their arms, and when connected to your company's LAN, all works fine, but as soon as they leave that LAN, their outgoing e-mail is rejected, right? That implies that they're all configured in POP3 mode, not in Exchange client mode. True?

    Well ... one way of addressing this would be to move your users' home internet connection to the company's ISP. That way, they could use the same SMTP relay from both home and work.

    Second, You'll probably want to avoid the hassle of setting up a company SMTP server for them to use, so that's no option.

    Third, in case you're running Version 2003 of Small Business Server, why not convert them to proper Exchange clients and let them use the RCP-over-HTTP feature? Relatively easy to configure, and hassle-free fom the user's point of view.

    Other than these options, there's nothing I can think of, really.

    Author Comment

    We found 2 ways of solving the problem in addition to your suggestions:

    1. When the person goes home, they change their outgoing server to their home ISP server. This allows them to send all their email without relay problems.

    2. Run VPN - ask users to connect thru remote access which solves the relay, and removes the need for users to change their settings.
    LVL 3

    Expert Comment

    Those two alternatives will work, but the process of changing the outgoing e-mail server is quite circumstantial because it needs to be automated (you won't want to ask the user to do it by hand each time), and it must be robust, too. Anything else will drive your 1st level support insane. Personally, I don't like this option at all.
    If you're going to go as "dirty" as this, you might as well set up a local DNS server and fake the MX record of your ISP's domain. Make it point to your local SMTP server, and you won't ever have to touch your e-mail client's configuration again. This is a nasty one, too, but it will run more stable.

    Running a VPN is by far the best solution if it's designed as a part of your overall IT strategy and embedded into a working, stable environment. Never use VPNs to fix a technical problem; you'll get yourself into trouble in the long run.

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