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Mail Servers

This guide will help you set up your own mail server using our services.

What is a mail server?

A mail server receives, stores and sends messages for a domain. A single mail server can host mailboxes for many users across multiple domains. Many people use third-party mail hosting services, but with Custom DNS, you can host mail for your own domain yourself and have total control over the mailboxes, mail policies, and anti-spam tools used by your server.

How do I set it up?

Please complete the following steps to learn how to use our services for your own mail server. (This guide assumes you will be using our Custom DNS service, but you may use our Dynamic DNS service as well.)

1. Install your mail server

The very first step is to install your mail server software. There are a number of proprietary solutions such as Microsoft Exchange, and a number of free, open source mail servers such as Exim and Sendmail. (Please note: DynDNS.com cannot provide support for service installation or setup. You will need to contact the software authors for more help.)

Once your server is installed and configured for your domain, and you have a few mailboxes created, you should test your mail server locally by performing a manual SMTP session over Telnet. Here is an example of a full test SMTP session with a mail server:

Please note that the above is purely an example, and the actual session may look different depending on your server. The most important things to notice in this manual SMTP session are:

• Valid 220 banner: Does your 220 banner feature the full hostname for your server (e.g. mail.mydomain.com, not mydomain.local or the IP address? If the server calls itself by an internal name or the direct IP, you may experience delivery issues.
• 250 response for a valid address: Does your server return a "good" response for RCPT TO an existing mailbox? If your server returns 550 User Unknown or 550 Relaying Denied for a valid mailbox at your domain, you will need to check your configuration.
• 550 response for invalid addresses: More importantly, does your server return 550 User Unknown during the RCPT TO stage for invalid mailboxes? If not, please see below for more information on recipient filtering and why it is important.

Once your server is responding properly and accepting mail for your domain, please move to the next step.

2. Configure port forwarding and firewalls

Now that your mail server is installed and running, the next step is to configure your network to allow remote access. To do this, you will need to configure your router's port forwarding settings. Please visit PortForward.com for a list of guides by router and service. By default, SMTP uses TCP on port 25. You will also need to allow this port in your firewall software, such as Windows Firewall or Norton Internet Security.

3. Test your network

When you have configured port forwarding in your router, you will need to test your network externally (from outside). To do this, get your network's external IP address from CheckIP, then have a friend try to Telnet to the IP address or use our Open Port Tool to test your network. If your network is configured properly, your friend should be able to receive the 220 banner from your server.

Please note: It is fairly common for ISPs to block port 25 for residential IP addresses. If your server appears inaccessible but you are positive that your network is configured correctly, you should configure your server for an alternate port (such as 2525 or 10025) and try again. If you are able to receive a successful connection on the alternate port, you can use services such as our MailHop Relay and MailHop Outbound to receive and send mail on alternate ports, respectively.

4. Configure your DNS

You will now need to configure your domain's DNS to receive mail. The best practice is to create a separate hostname for your mail server, such as mail.mydomain.com, then create MX (Mail eXchanger) records that tell sending servers to deliver mail to this host. You can learn more about MX records, mail exchangers and DNS here.

There are two ways to add the necessary host and MX record in Custom DNS:

• In Standard Interface: Create mail.mydomain.com using the Add Hostname button and assign it to your network's IP address, then click Edit MX List and enter the new hostname into the field. Our wizard will create the necessary MX record for you at the proper Preference value.
• In Expert Interface: Add the following two records:
  • Host: mail
  • TTL: 60
  • Type: A
  • Data: (Your IP address)
    
    
  • Host: (blank)
  • TTL: 43200
  • Type: MX
  • Data: 10 mail.mydomain.com

The 10 in your MX record's data field indicates its Preference: the lower the number, the higher the priority. If you want to add a secondary server later, such as our MailHop Backup MX service, you would add it with a lower Preference such as 20.

Once your new record has a change to propagate (which should only take a few minutes if you have no MX records at all), you should be able to receive mail at your domain.

5. Install an update client

The last step is to configure an update client, which will keep your new Dynamic DNS host up-to-date with your network's external IP address. If you do not have a hardware update client, you can install a software update client on a computer anywhere in the network (typically your server computer). We recommend using a software client whenever possible, since they are easier to troubleshoot and configure than hardware update clients.

Troubleshooting

My server is running, but I can't reach it from outside my network.

This problem is usually related to port forwarding. Ensure that your router is properly configured to forward the necessary ports for your software. You can learn more about port forwarding here. If you are still having trouble, please see our detailed Why Can't I Connect to My Server? troubleshooting guide for more help.

As noted above, many ISPs block port 25 on residential connections. Please set your mail server to an alternate port such as 2525 or 10025, then try again; if the alternate port works, your ISP is blocking SMTP and you will need to use MailHop Relay to receive mail and MailHop Outbound to send outgoing mail around the blocking.

I keep getting rejections for having a dynamic IP address.

Some mail hosting providers such as AOL and Hotmail block messages from dynamic IP addresses. They base their blocking criteria on two things:

• Your IP is from a dynamic pool: Most residential connections draw from pools of dynamic IP addressess which the provider has specifically blacklisted.
• Your reverse DNS is invalid: Most residential IP addresses reverse-resolve to provider-specific zones, such as 1.2.3.4 resolving to c-4-3-2-1.node.state.isp.com. A proper mail server resolves both forward (mail.domain.com to 1.2.3.4) and reverse (1.2.3.4 to mail.domain.com).

If both of these criteria are not met, the mail is rejected. To prevent these rejections, you can either upgrade your connection to a costly static IP address, or use our MailHop Outbound service. Outbound is an outgoing SMTP relay through which your server can deliver its mail unimpeded, as the reverse DNS checks are performed on the most recent sender (in this case, our servers, which have static IPs and reverse DNS) instead of the origin.

I have a static IP address. How to I configure reverse dns with Custom DNS?

Please see our Reverse DNS in Custom DNS article for more information.

Why can't I use a CNAME with my MX record?

Per RFC 2181, MX records may never use a CNAME or a direct IP address, only a host record. Directly from section 10.3 itself:

The domain name used as the value of a NS resource record, or part of the value of a MX resource record must not be an alias. ... This domain name must have as its value one or more address records. Currently those will be A records, ... It can also have other RRs, but never a CNAME RR.

If a mail hosting provider specifies a CNAME, simply perform a DNS query for the record and use the host record to which it resolves instead.

Do I technically need an MX record?

Technically, no. If a sending server tries to deliver mail to a domain that has no MX records, the sending server generates a temporary MX record assigned to the domain itself, and tries to deliver it there (e.g. senders for user@example.com would connect to example.com on port 25 to deliver the messages).

However, not all mail servers follow SMTP specifications correctly, including older versions of Exchange. To ensure you do not lose any mail, it is always recommended to create an MX record for your domain.

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