Exchange 2003 cannot send emails to Comcast

Posted on 2011-10-21
Last Modified: 2012-05-12
I have a client using XO as their ISP. They are running SBS 2003 and are having problems sending emails to Comcast accounts. XO doesn't offer a smarthost option and doesn't have an option to add an SPF record. We have setup a RDNS record.

At this point XO is not willing, or able, to do anything more to help troubleshoot this problem. As a workaround, I configured their domain to send emails using, which worked fine with one exception. We have a few people that have their company email forwarded to an external account. Since requires that each sending email address is authenticated prior to being able to send, all of the forwards from domains outside of the network fail with an 'not an authorized user' error.

Ideally I'd like for this to work like all of the dozens of other SBS servers we support.

Anyone have a brilliant and cunning plan?


Question by:geoffdavis
    LVL 21

    Expert Comment

    Unless XO also manages forward DNS for your domains, then XO has nothing to do with adding your SPF record.

    If for example your domain registrar is godaddy, and they are still authoritative for your domain, that is where you would add the SPF TXT record for your domain.

    Author Comment

    Papertrip - thanks for the response.

    Do you believe that the SPF record would prevent emails from making it to Comcast?

    BTW: We use for DNS for all of our small clients and are able to add SPF records there. We use them because they queue up email if and when the server is down.
    LVL 21

    Accepted Solution

    Having errors or missing sending IP's in your SPF record could most definitely prevent Comcast (and many others) to not accept your mails.  There are other factors that could be in play here however, such as a mismatching A/PTR record of your sending servers, if you are blacklisted, etc.  Run your domain/servers through to get some of the basics checked out for you.

    For all mail from any domain, you should always use SPF records, and preferably also sign with DKIM.

    If you use now for all your "normal" DNS records, then that is where you will be adding the SPF records for your domain(s).
    LVL 21

    Expert Comment

    Hi, is this still an issue?

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