Announcement

Collapse
No announcement yet.

PTR advice

Collapse
X
  • Filter
  • Time
  • Show
Clear All
new posts

  • PTR advice

    We’re looking for some advice before creating a PTR.

    The majority of our outbound mail is sent from our Exchange 2010 CAS/Hub, the Send Connector uses mail.domain.co.uk (which matches our MX record)

    We relay outbound mail via our ISP’s Smart Host. All inbound mail hits the same CAS/Hub.

    However we have one external IP for our MX record and a different external IP for all of the various associated A records (outlook, owa, autodiscover etc)

    Both of the external IPs route to the same CAS/Hub, but which IP do we use for the PTR?

    Advise differs between using the MX Record IP and using a hostname IP.

    Secondly, we also send outbound mail directly from webservers (using IIS) to our ISPs Smart Host and this mail has a different/unique originating IP to our Exchange mail – so does this mean that adding a PTR for Exchange could risk interfering with outbound mail flow from our webservers?

    Any advice appreciated.

  • #2
    Re: PTR advice

    For the PTR, you use whatever the internet can see.
    Therefore from the Exchange server, either browse to one of the what is my IP address sites, or telnet in to a remote Exchange server and issue a ehlo.

    If it isn't the correct address, then you need to look at your NAT configuration.

    If you are sending email from the web hosts, then they will need their own PTR.

    There is no connection to the MX record though - it is all down to a matching pair of A record and PTR on the same IP address.
    The only thing to watch with web hosts is that they are included in your SPF records.

    Although it could be argued that if you are using your ISPs SMTP server, you don't need a PTR at all.

    Simon.
    --
    Simon Butler
    Exchange MVP

    Blog: http://blog.sembee.co.uk/
    More Exchange Content: http://exchange.sembee.info/
    Exchange Resources List: http://exbpa.com/
    In the UK? Hire me: http://www.sembee.co.uk/

    Sembee is a registered trademark, used here with permission.

    Comment


    • #3
      Re: PTR advice

      Thanks for the reply. I do get your point re the ISP Smart Host but they’ve requested that we also create our own PTR (their relay already has a PTR).

      For the hostname that I’ll be using in the Exchange PTR, do I also need to create a corresponding A record for the hostname.domain.co.uk ? or doesn't this matter so long as my SMTP banner already has an A record (i.e. mail.domain.co.uk)

      And for the webserver PTR (as it uses a different IP) the machine is a workgroup member not a domain member, so for this PTR do I specify just the hostname instead of any canonical name?

      Thanks again Simon.

      Comment


      • #4
        Re: PTR advice

        The PTR must resolve to the host on the internet.
        What you put in doesn't have to connect to the server's real name, as long as it resolves correctly.
        In most cases the SMTP banner should also match the PTR, so that all three checks are consistent.

        Simon.
        --
        Simon Butler
        Exchange MVP

        Blog: http://blog.sembee.co.uk/
        More Exchange Content: http://exchange.sembee.info/
        Exchange Resources List: http://exbpa.com/
        In the UK? Hire me: http://www.sembee.co.uk/

        Sembee is a registered trademark, used here with permission.

        Comment


        • #5
          Re: PTR advice

          OK so now I'm really confused.
          A recipient mailserver will obviosuly see our originating IP to which they perform the rDNS lookup against, but what does the lookup actually compare the hostname in the PTR with? Does the lookup expect the PTR hostname to match the hostname in the mail header?
          I know I need three PTRs because our mail is sent from three different sources each with a different external IP.
          PTR number 1
          Outbound mail from Exchange currently display hostname.domain.local in the header.
          Do I use hostname.domain.co.uk for the PTR and do I need a corresponding A record for the hostname.domain.co.uk?
          PTR number 2
          Outbound mail from IIS currently just gives the hostname in the header (it's a workgroup member)
          Do I use just the hostname on its own as the PTR, and I can't create a corresponding A record for a workgroup member (if one is needed)
          PTR number 3
          Outbound mail from a SMTP relay at a remote site which sends direclty to the ISP Smart Host.
          This gives hostname.domain.local in the header, so do I use hostname.domain.co.uk in the PTR?
          I know I can manipulate the DNS suffix but surely this isn't normally required for a PTR?
          Thanks again (I told you I was confused )

          Comment


          • #6
            Re: PTR advice

            You send an email from server mail.example.com
            The receiving server sees the connection coming from mail.example.com with IP address of 123.123.123.123.
            The receiving server then does a lookup on 123.123.123.123 to see if mail.example.com is set as the PTR.

            Some servers will also look at the SMTP banner, which is set on the Send Connector. That should be set to match.

            Therefore if you have three servers you should have a unique host name for each one (mail1.example.com, mail2.example.com etc). The relevant PTR needs to be configured.

            Then configure a Send Connector for each server with the correct source server and FQDN.

            In IIS, on the SMTP server config, under Advanced you can set the FQDN used for connections to the remote server. For IIS only, if you telnet to port 25 of the server you will see the banner (doesn't work for Exchange 2007 and higher).

            Simon.
            --
            Simon Butler
            Exchange MVP

            Blog: http://blog.sembee.co.uk/
            More Exchange Content: http://exchange.sembee.info/
            Exchange Resources List: http://exbpa.com/
            In the UK? Hire me: http://www.sembee.co.uk/

            Sembee is a registered trademark, used here with permission.

            Comment

            Working...
            X