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POP3 with 1 SBS, 1 domain and 2 sites!

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  • POP3 with 1 SBS, 1 domain and 2 sites!

    Hi All,

    I've having some mail delivery problems with SBS, here's the set-up:

    Company has two sites, all the users on both sites use the same email address (domain name). All email accounts are POP3 to a external company.

    One site decided they wanted SBS 2003 but the other decided they didn't, so I installed SBS and the POP connector and they are happily sending and receiving mail.

    The problem comes to when they try and email users on the other site, I think SBS looks internally first for the user they want to mail but cant find them and returns

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

    Sent: 16/09/2008 15:32

    The following recipient(s) could not be reached:

    Is there a way around this so SBS sends it straight out and doest check internally, maybe by creating the user in AD and forwarding the mail??? I'm a little lost with this and new to SBS so not really sure what I can do so any advise would be much appreciated.



  • #2
    Re: POP3 with 1 SBS, 1 domain and 2 sites!

    You have to understand some fundamentals about mail routing. Your SBS is responsible for delivery of mail to your domain (let's call it Assume UserA is on Site1 with the SBS and UserB is on Site2.
    But you also have an external server responsible for mail for your domain.
    So someone sends mail to [email protected]. MX recordsin DNS in the big wide world send the mail to the external server. Your POP3 Connector on SBS pulls it down and puts in UserA's mailbox. I assume UserB goes directly to the external mail server and gets his mail that way.
    So far, so good, that is what you want.
    UserA sending mail outside the domain may have a problem if the recipient does a reverse lookup (and many do to avoid spam). The reverse lookup will reveal that mail's server is the external but the mail will come from your SBS IP address. The way round that is to use the external mail server as your "smarthost" and it will actually deliver your mail.
    Your real problem will come - and this is what you were asking about - it when UserA wants to send to UserB. UserA uses the SBS to send and the SBS sees you want to send to Since the SBS considers itself responsible for, it looks for UserB's mailbox for delivery, and naturally doesn't find it. Hence the NDR you receive.
    The solution IMHO is to make your SBS use SMTP and receive all mail for your domain. Drop the POP3 connector and get all your users at the second site to collect their mail from your SBS - by OWA/OMA or RPC over HTTPS.

    Steven Teiger [SBS-MVP(2003-2009)]
    Iím honoured to have been selected for the SMB 150 list for 2013. This is the third time in succession (no logo available for 2011) that I have been honoured with this award.

    We donít stop playing because we grow old, we grow old because we stop playing.


    • #3
      Re: POP3 with 1 SBS, 1 domain and 2 sites!

      Hi teiger, Thanks for the reply you've got it spot on with how our traffic is routed and the issue we have. I think your exactly right with your recommendation and to be honest its something I had considered but wanted some other opinions first. I think I'll probably go down the RPC over HTTPS route, thanks again.