How does Autodiscover works for external clients?


We have an Exchange 2007 server published over internet with a public IP and DNS records. Do we need to register a DNS record for Autodiscover in order to make it available for external clients? If yes, what type of DNS record required?

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Grant BerezanSenior Network EngineerCommented:
You do need a DNS record, usually a subdomain, for, but in order for Exchange to properly get the Autodiscover settings,et al., you need to purchase an SSL certificate with multiple names in it. The cert needs to have your internal domain name, your external domainname if you host a secure website, your email server internal domain name, your external mail domain name, the hostname of the internal email server and the autodiscover. As an Example:

The reason you put in the internal server name is that you use it for authenticating internal Outlook client's easier, and you require it for standard RPC over HTTP proxy.
imranrftAuthor Commented:
So, a wildcard certificate will be OK?

And how can we buy a certificate with many names in it? I mean, do the certificate providers give us the flexibility to add multiple names?


There are two ways to make Autodiscover work.

The first (and most common method) is a DNS A or CNAME record - autodiscover - which maps to the public IP/alias of your outward facing Client Access Server/farm.

The second is to use a DNS SRV resource record to reference the location of the autodiscover services - this is a good workaround to the multi-name certificate requirement, but it causes many, many issues particularly down to the fact many DNS providers do not support SRV records. For a minimal expense, you can upgrade to a SAN/UC certificate and save the hassle of ever needing the SRV record approach.

>> how can we buy a certificate with many names in it? I mean, do the certificate providers give us the flexibility to add multiple names

Most major suppliers offer what is known as a SAN (Subject Alternative Name) - also known as UC (Unified Communications) - certificate. These can have multiple names listed and have a "default" name (the common name) used for any device which does not support the SAN format. The common name should always be your main public OWA/Exchange ActiveSync URL - if a mobile device, for example, cannot read SANs, it is less likely to have SSL issues in this set up.

The SAN names noted above are the general recommendation. You do not NEED internal server names on the certificate (I always set mine up without them, so the certificate is not server dependent). However, using internal names makes it easier and eliminates the hassle of playing with URLs in Exchange Powershell.

GoDaddy, and their many affiliates, offer SAN/UC certificates at an affordable price.

>> a wildcard certificate will be OK

Wildcard certificates work to a point. They will cover your back for and They will not be valid for the internal server and domain names, so some URLs on Virtual Directories might need updating if you don't want Outlook 2007+ showing certificate prompts internally. Also, be aware that Windows Mobile 5 devices did not support wildcard certificates, making it a particular sticking point back then. There may be other devices on the market today in a similar position.

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I would strongly recommend you to read the below Autodiscover Whitepaper as it gives all the options to configure Autodiscover over the Internet and it also explains how to configure the same.

White Paper: Exchange 2007 Autodiscover Service
And regards to Wild card certificate, Matt has already explained you about it. Also you can refer to the below article,

Wildcard Certificate Causes Client Connectivity Issues for Outlook Anywhere
imranrftAuthor Commented:
Thanks for the info guys.

By the way, what is needed to make AutoDiscover work internally in the first place?

Autodiscover is a rather complex system, but at a high level you need to ensure the appropriate DNS records are created *and can be accessed* internally.

Also, you must ensure a valid third-party (trusted) SSL certificate is in place on the Exchange Server and that your virtual directory URLs are correct. If the URLs on the VDirs are incorrect, autodiscover will publish incorrect information which will cause issues with the availability service, Out of Office assistant, OAB downloads and many other things.

imranrftAuthor Commented:
All of you!

Thank you very much for the help..
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