In most situations adding a second email domain is simply just a matter of configuring the necessary mail flow. However, in situations such as an acquisition or merger you may need users to configure Outlook with an email domain that is different from the one configured in your autodiscover URI. This is especially true for companies that offer hosted Exchange in a multi-tenancy business model.
In this article we take a look at a couple case studies where an SRV record might be preferred over adding additional names to a certificate. We then explore how to configure an SRV record in a popular DNS management system. Finally we look at two different ways to test that SRV record.
Case Study 1 : Acquisitions and Divestiture
One solution is to simply add each domain to your UC / SAN certificate (also called a multi-domain certificate). This may seem like a quick and easy solution but it all depends on volume. Re-keying your certificate for a one time acquisition or merger may seem like a minute task. But consider a company that frequently acquires or divests other companies. You may find yourself re-keying that certificate every couple of months. This may still seem trivial but consider the size of your environment. If you have a large Exchange deployment with dozens of servers and multiple load balancers then each will need the new certificate every time it is re-keyed. This pales in comparison to the single SRV record that can be easily added to the new domain. It not only saves you time, but also money. Adding each domain may incur additional charges. Some certificate providers even charge a fee for re-keying a certificate.
Case Study 2 : Multi-tenant hosted Exchange providers
With a hosted Exchange provider the acquisition and departure of clients is likely to be even more volatile. That said, you don’t want to be re-keying your certificate every time you on-board or off-board a client. Adding each domain to your certificate will eventually become cost prohibitive affecting your bottom line. Like any business your bottom line is important. So choosing the SRV redirect method over a cost prohibitive multi-domain certificate is more attractive (and also simpler to configure).
For the purposes of this article ExchangeServerGeek has recently acquired SuperTekBoy. STB users have an email address of SuperTekBoy.com. Where as ESG users have an email address of ExchangeServerGeek.com. Mail data from STB has already been migrated to the ESG. The company requires STB users to keep using their SuperTekBoy.com email addresses to configure their Outlook profiles. The company does not want to make any changes to its current SSL certificate as this will incur additional fees. The Exchange administrator determines the best solution is to configure an SRV record.