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Thread: inverse DNS question

  1. #1
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    Default inverse DNS question

    Hello,
    We have set up a small install of zimbra. Some of our mails are getting rejectec and I believe it has to do with the inverse lookup check that some servers do.
    From the admin gui I can se that there are a couple of message that stay in the cue. When I check the error it is usually related to the name of the sender and its IP (sorry I don't have access to the exact error rigth now).
    Our configuration is very basic. We are behind a firewall provided by our ISP which we do not have much access to. In our local network there is a zimbra server and a DNS for local computers.
    Since I have to use (right?) the ip of the router as mail server in our external DNS (provided by the company we got our domain from) I do not know how or if I can configure the system so that some of the mail is not rejected.
    Any ideas?

  2. #2
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    Well for starters you should be running a Wiki :: Split DNS architecture as you are behind a firewall on a private IP. Now if you already have a local DNS server then you just need to ensure that a valid A and MX record are present for your domain. You will also need to check your external MX and A record and ensure that a valid reverse record is present for your server. If not then I would recommend that you use your ISPs SMTP smarthost to send out email, which can be setup from within the Admin GUI. This will pretty much ensure your domain/server does not get marked as a SPAM source.

  3. #3
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    Thank you for your time. If you do not mind bear with me for a minute as I'm not that familiar with dns procedures.
    From what I understand from other posts, the split DNS architecture objective is just to be able to resolve an internal IP for the zimbra server from the computers behind a network (let's say 192.168.88.3) and an external IP for the same server from the computers out (let's say 212.85.12.65). This already works (I think).
    If I ping our mail server from within our network I would get 192.168.88.3. If I do a reverse lookup of that address I obiously get our mail server. So far so good.
    Then from the ourside, if I ping our mail server I get the public address (the address of the ISP's router 212.85...). This router redirects mail ports to the mail server. When I do an inverse lookup of the public IP I get the name of the router. I guess this is to be spected but that is also my problem.
    I'm thinking that the problem may be with the records on the external DNS. This DNS has a control web console in which I can set up MX, A, TXT records etc. Our MX record points to the public IP (the router) and there is also an A record with the name of the mail server (same as internal one). What I do not have is a way of setting up reverse lookup addresses. Nor that I think it would do any good because I'm asuming that is on another DNS server property of our ISP since we have not set it up (Am I correct?).
    So, do we have to contact our ISP to try to change our reverse look up? (I think it is highly unlikely that they would do so). Is there any other solution?
    What do you mean by SMTP smarthost? You mean an account on their mail server to send mail trought?
    Thank's a lot for your time

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    Quote Originally Posted by alberto View Post
    You mean an account on their mail server to send mail trought?
    That is correct. So I guess something like smtp.myisp.net. They should have the necessary DNS records in place. I do this on my home server and have never been blacklisted.

    Quote Originally Posted by alberto View Post
    Thank's a lot for your time
    Its a pleasure

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