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Using an Alias as an MX record??

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  • Using an Alias as an MX record??

    This is a bit strange as I haven't encountered it before.

    One of our customers has their MX record set as mail.theirdomain.com. Now when I ping this, it shows the IP of our mail device which is actually on the address mailgate.ourdomain.com.

    How have they set this up? I have been told to ask them to change their MX records as we are moving onto new mail filtering devices, at new addresses. If they request their web host alters the MX records, will an NSLOOKUP still show the mail.theirdomain.com or will that be removed and replaced with the new records?

    I guess what I am getting at, is will that record be unaffected as it's something else like an A record or a CNAME or something that's been pointed at the IP the mail should go to if the hosting co change their MX's? Is there something else that I need to get them to ask for?

    Sorry if that doesn't make much sense, I've tried my best to explain it.

  • #2
    Re: Using an Alias as an MX record??

    Their MX record for their mail domain, should point to an A-record (or CNAME) that points to an SMTP endpoint for their mail environment.
    MX->mail.theirdomain.com->IP of their mailserver
    At least that is sort of the norm.

    But it seems as if they have done this:
    MX->mailgate.ourdomain.com-> your mailserver

    Correct?
    Is this the only MX record they have? Does your mailgate forward their mail to their mail server and you've agreed to this? If you provide anti-spam/malware features, then that is not unexpected.

    MX records always point towards existing A-records etc., not towards IP addresses. So if you change the A-record to point to a new IP Address, you will eventually be good. However, please note the Time-To-Live i.e. the time it could take for changes to propagate. It could mean that mail will be delayed or won't arrive.

    Does this answer your question?

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    • #3
      Re: Using an Alias as an MX record??

      Hmmm sort of. It's just strange because all of the other customers MX records point directly at the mailgate.ourdomain.com.

      It is the only MX record they have and yes, we do provide them this service. I just find it odd that they are set up differently, and I am worried that when they request the MX change, their hosting provider might screw something up.

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      • #4
        Re: Using an Alias as an MX record??

        Originally posted by Jay Cartay View Post
        Hmmm sort of. It's just strange because all of the other customers MX records point directly at the mailgate.ourdomain.com.

        It is the only MX record they have and yes, we do provide them this service. I just find it odd that they are set up differently, and I am worried that when they request the MX change, their hosting provider might screw something up.
        Ah, right. I understand the situation better now. Both configurations will work, but their config is not really robust when your IP address changes.

        I would advise them to point their MX record to your mailserver FQDN (i.e. mailgate.ourdomain.com) and not use their own A-record pointing towards the IP address of your server. The latter is changing (if I understand you correctly), so inbound mailflow would be impacted for them.

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        • #5
          Re: Using an Alias as an MX record??

          I had a customer that did this as well. The downside is that if you change the ip address of your server then their email is not going to get to it unless they change their A record to match.

          Other than that there's nothing technically wrong with it, but my recommendation would be that they change their MX record to use your A record instead of theirs.

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