i am trying to configure Exchange Server 2010 on Windows Server 2008 R2 to receive emails from the internet following the danscourses tutorials:

and i followed this video for the DNS & MX records:


i don't have any windows administration skills, and i am stuck with the DNS configuration. and the following are my domain configuration i got from the hosting. My Domain Configuration

following are the steps i made:

1- Add new name server:

add > ns1.centors.com ip > Exchange Server Public IP:

2- Change the A record

change it to point to the public ip address > Exchange Server Public IP:

3- New cname record for www

and make it resolve to centors.com

4- New mx record for mail.centors.com

5- New A record for mail.centors.com:

name: mail ip: Exchange Server Public IP:

6- new A record for ns1:

ip: Exchange Server Public IP:

7- i made port forward in the router for SMTP and POP3 to the exchange server local ip address.

ISSUE: i have a user account in the active directory, and the user is member of the domain, the user is myuser@centors.com and when trying to login with this account in outlook 2010 on other machine using following data:

  • account type: POP3
  • incoming mail server: mail.centors.com
  • outgoing mail server: mail.centors.com

i always get the error: Authorization failed, check your server settings.

please advise what's wrong with the configuration, thanks in advance.

  • Learning DNS from a video. The end of the world is really close. – bortzmeyer Sep 23 '12 at 14:43
  • @bortzmeyer, i am a developer and i have to do this administration task quickly, what should i do ? – Mahmoud Saleh Sep 24 '12 at 8:08

There are several things wrong I can see here:

  1. Just so you're clear, a DNS domain on the Internet is not necessarily the same domain you're using in Active Directory. It can be the same, but more often than not (in smaller organizations), you'll choose to use a domain such as centors.local* that's only applicable/resolvable internally by your Active Directory DNS servers.

    Your Internet domain is usually (and really should) be handled by an external DNS server (and typically your domain registrar or a 3rd party company that specializes in DNS like no-ip.com or dnsmadeeasy.com). This is because:

    a) there's usually no beneficial reason for handling your own public authoritative DNS server unless you're a large enterprise or have atypical/legacy reasons to do so; I'm confidently going to say that you don't have any of these requirements.

    b) managing your own Internet facing DNS server is not easy: you need to make sure it's always up, has geographical redundancy (multiple servers, in different physical locations) and is secure (DNS poisoning and amplification attacks ad naseum).

  2. You likely don't need to change your Nameserver (NS) records. These are used to tell the world what DNS servers are authoritative for your Internet domain (centors.com). When you register a domain at networksolutions.com, godaddy.com, etc. they typically offer authoritative nameservers for you (and thus have already assigned their NS records to your domain), so all you need to do is log in to your DNS control panel and modify the records (the zone). Typically a small business will only ever need to create/modify A, CNAME, MX, and possibly TXT (for SPF) records.

  3. To get your mail flowing properly, you need to create an A record and an MX record: typically the A record would be mail.centors.com, and this A record would resolve to the publicly-accessible IP address (assuming that your Exchange Server is either NAT'ed behind or assigned itself (usually the former as the Exchange Server will be on the LAN behind the router/firewall). For the MX record, you would create an entry with a number to denote order of priority. Since you only have (I'm assuming) one mail server, you would just add mail.centors.com with a priority of 5 to your MX records.

  4. As for Active Directory authentication issue, I'm assuming that you haven't configured POP3 yet on your Mail Server. I would strongly recommend you don't add POP3 support unless you have some legacy reasons why. It's a terribly inefficient way of handling mail, especially if you have an Exchange Server. If your Outlook 2010 client is on the LAN (and is on a workstation that's joined to your Active Directory domain), you want to add an Exchange account as the mail type, not POP3.

*As for your DNS in Active Directory, I'm not sure how far you've gotten with it, but I would recommend you change your Active Directory domain to something that you won't use publicly like corp.centors.com or centors.local (the latter is not recommended by Microsoft because it does not guarantee that the domain is unique and if you ever merged with another "centors" you would need to change your domain; it's up to you whether that's a risk or not).

  • thanks for detailed answer, since i already have an A record and mx record for the mail, do i have to remove the configuration in the first 3 stpes ? also i tried to create an exchange email account in outlook (on other machine) and entered the server as centors.com and the username myuser@centors.com but i am getting the error: connection to microsoft exchange is unavailable outlook must be online or connected to complete the action, please advise. – Mahmoud Saleh Sep 25 '12 at 9:53
  • ,the ping for mail.centors.com works fine, my issue now is that i can't login to my exchange email accounts, and i posted an issue about it here serverfault.com/questions/432092/… – Mahmoud Saleh Sep 26 '12 at 9:23

Connection to a POP3 server never uses the MX records. Now, for the other DNS records, just typing "ping mail.centors.com" in the command terminal will tell you if the DNS setup is OK and if you get the right IP address. If not, edit your question to mention that.

Network debugging should not be done by huge and complicated user clients like Outlook but by low-level sysadmin tools like ping, traceroute or telnet because they give you access to the raw information.

As of today, mail.centors.com is an alias to pop.secureserver.net. which lives at

  • the ping for mail.centors.com works fine, my issue now is that i can't login to my exchange email accounts, and i posted an issue about it here serverfault.com/questions/432092/… – Mahmoud Saleh Sep 26 '12 at 8:54
  • In that case, it is not a DNS issue at all and I suggest changing the subject – bortzmeyer Sep 29 '12 at 20:15

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