Exchange with a Dynamic IP Address

Having email delivered direct to your Exchange server by SMTP instead of via a POP3 connector is the way that Exchange was designed to work and is the most efficient and fast way of getting email.

However a common complaint is that the server is on a Dynamic IP address, making MX records difficult to set. The IP address is constantly changing and the Internet DNS system cannot keep up.

By making use of a Dynamic DNS service you can have SMTP delivery to your email server. If you would like to know more about Dynamic DNS services and how they work, please click here.

To Make a Dynamic DNS System work for your Exchange Solution:

1. Sign up for a Dynamic DNS Account with one of the providers. You can use one of their domain names for the account as this is just for MX records. However do use something sensible or that identifies your company name for an account name as it can be seen on the Internet if people are checking up on your settings.
   For providers see the list at DMOZ Directory:
   https://www.dmoz.org/Computers/Internet/Protocols/DNS/Service_Providers/Dynamic_DNS/
2. Install an updater tool on your Exchange server. This will ensure that the IP address stays up to date. The Dynamic DNS provider should have a list of updater tools that work for their service. Try and get one that operates as a service. This will mean that it continues to work even if there is no one logged in to the server. You may already have the service on your router - so check there as well. 
3. Verify that the updater tool is working through at least one IP address change.
4. Change your MX record for your domain to point to your new Dynamic DNS name.

As long as the information with the Dynamic DNS provider is kept up to date the Internet will always be able to find your machine to deliver email despite the IP address changing.

More About MX Records

There seems to be some confusion over configuration of MX Records. Hopefully these short bytes will help you understand MX record configuration.

• MX records are always two parts - the host and the record itself.
  • You create the host with an IP address.
  • Then you point the MX record at this host.
• An MX Record cannot be an IP address, but it can be a host name that is outside of your domain name.
  For example the MX record for example.com could be mail.example.net
• All an MX record does tell other email servers where to deliver email destined for example.com therefore it doesn't matter which domain it belongs to.

SMTP Connectors (Exchange 2003) / Send Connectors (Exchange 2007/2010)

You do NOT need an SMTP connector for receiving email via SMTP. SMTP connectors are used just for outbound email.

However if you are on a dynamic IP address you will have problems getting email delivered to some remote sites. Therefore you should setup an SMTP or Send Connector to route outbound email via your ISPs SMTP Server. More information on using SMTP Connectors for Exchange 2003 can be found here, Send Connectors for Exchange 2007 are here.

SSL Certificates and Using Your Own Domain

If you want to issue commercial SSL certificates, for example so that you can use Outlook Anywhere/RPC over HTTPS, OWA, Exchange ActiveSync etc, then it is much easier to get them issued to your own domain.
Therefore the simple way round that is to put a CNAME in your own domain that points to the dynamic IP address host. For example, you would CNAME remote.example.com to domain.dynamicip.net. If someone enters https://remote.example.com in to their browser it will resolve correctly and will not generate SSL errors.
You could technically use the same practise for your MX records, but this is not best practise as it requires an additional DNS lookup and will cause some DNS record services to log a warning or failure.

Having the Dynamic DNS host name resolve internally.

If you want your dynamic DNS host name to resolve internally to the server, then you need to configure a single host replacement split DNS system.