For Exchange 2000 and Exchange 2003 prior Service Pack 1, the building of an URL suitable for WebDAV requests against a users mailbox is a rather complicated thing. A solution for this is descrbied under the section Solution.

From Exchange 2003 SP 1 onwards, you can just use his SMTP address to get access to his mailbox. For example, to access the mailbox of John Doe (jdoe@contoso.com) you would use the url

http://<myserver>/exchange/jdoe@contoso.com

To build the webaddress, you must do the following:

1. If you only have a domain\username, not the distinguished name of the user, you must first get the latter one. See this aricle how to retrieve the name.
2. Get the directory entry with the distinguished name of the user
3. From that object, retrieve the property homemdb. This property contains the distinguished name of the mailbox store.
4. Retrieve the directory entry of the mailbox store.
5. From this object, retrieve the property named msExchOwningServer. This is the distinguished name of the Exchange server that hosts the mailbox.
6. Get the root of the http virtual server on the exchange server. The distinguished name is CN=http, CN=Protocols, <distinguished name of the exchange server>.
7. Search for all http virtual server (LDAP filter: (objectClass=protocolCfgHttpServer), Scope: OneLevel, retrieve these properties: msExchServerBindings, msExchDefaultDomain).
8. From this list, retrieve the default SMTP server. It's the one without the attribute msExchDefaultDomain.
9. Get the default SMTP domain of the organization:
1. Open the node CN=Default Policy, CN=Recipient Policies, CN=<Name of your organization>, CN=Microsoft Exchange, CN=Services,<Distinguished name of the configuration naming context>.
2. Retrieve the property gatewayProxy. This is a multi-valued property that contains the default addresses of the organization.
3. Check each of the entries in that list. If it starts with SMTP:, you have found it.
10. Get the property proxyAddresses from the directory object of the user. This is a multi-valued properties that contains all addresses that are assigned to the user. Each entry has the following consists of a protocol identifier and an address entry. For example:
    SMTP:john.doe@example.com
    If the protocol identifier is all uppercase, it is the default entry for that protocol.
11. Iterate through the list of assigned addresses and search for the SMTP address which domain part matches with the default SMTP retrieved above.
12. Select the correct HTTP Server:
• If you found an email address corresponding to the default SMTP policy, extract the alias from the found address. For the above example the alias would be john.doe.  The correct HTTP server to use is the default HTTP Server
• If there is no smtp address matching the default policy, iterate through the list of proxy addresses again, and do the following, if it is an SMTP address:

1. Extract the alias and the domain from the address.

2. Iterate through the list of virtual HTTP server and check the property msExchDefaultDomain of each entry. If it matches the domain of the users address domain, you have found the correct http server.

13. Get the property msExchServerBindings from the selected HTTP server node. This entry has the following structure:
    IPAddress:Port:Servername
    The first and the last part of the string can be empty, like in this example:
    :80:
14. Depending on the content of this field, you can now build the desired url:
• If the servername of the msExchServerBindings property is not empty, build the OWA url like this:
  http://<Servername>:<Port>/exchange/<Alias>
• If the servername is empty, but an ipaddress is present, build the OWA url like this:
  http://<IPAddress>:<Port>/exchange/<Alias>
• If both, the servername and the ipaddress fields are empty, get the ipaddress for the exchange server:
1. From the node of the exchange server, retrieve the property networkaddress.
2. Iterate through this property and retrieve the value which starts with ncacn_ip_tcp:.
3. Now, build the url with the above scheme, using the just found ip address.

To get the contents of a distribution list, make a GET request to the URL of the distribution list with the query-string set to Cmd=viewmembers. The User-Agent header must be set to Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.2; .NET CLR 1.1.4322) so that the Exchange ISAPI filter knows the client can handle an xml response.
The response will look like this:

The member is is espacially important when removing members from a distribution list, because it must be passed along with the request.

To add a new member to a distritubion list, make a POST request to the URL of the list and specify this body within the request:

Again, the User-Agent field must be set to the value mentioned above.

On success, you will receive a HTTP/1.1 302 Moved Temporarily message that point to the url of the list with the querystring set to Cmd = viewmembers.

To remove a member from the list, make a POST request with the following body within the request:

Be sure to set the member id to the id of the entry you want to remove. When successful, you will receive the same response as above.

This article was formerly published under the title "Get Free/Busy data for an Exchange 2000/2003 user via HTTP requests".

For each user, Exchange stores a free/busy data on the server. Exchange 2000 and 2003 store the free/busy information in a public folder. Exchange 2007 can also do this for compatibility, but it offers a far more convenient way to get the availability, namely a WebService.

With Exchange 2000/2003 we are left with two options to read the availability data: Use OWA and pretend to be an Internet Explorer 6 or later, or access the free/busy data directly. I will cover each option in this arcticle.

The availability information is stored in the NON_IPM_SUBTREE folder hierarchy below the Public Folders hierarchy in a folder called EX:/o=<Name of your organization>. For each administrative group, there is a subfolder. Each one of those folders contains the availability data for the users associated with that administrative group.

The question is: How do I get the right item in those folder for a particular user?

The answer comes in the form of the legacyExchangeDistinguishedName property from the Active Directory object of the user.

ADSIEdit showing the legacyExchangeDistinguishedName of a user (click to enlarge)

Once you have the legacyExchangeDistinguishedName of a user, you'll have to split it up. From position 0 to the slash ("/") before cn=Recipients and from that index to the end of the string. To construct the item url, you can use this method:

Since the legacyExchangeDistinguishedName contains a slash in the item name, you must encode it with is unicode representation, _xF8FF_, otherwise Exchange would treat it as a folder delimiter.

Once you have the url to the free/busy item, you can issue a PROPFIND on the item and retrieve these properties:

• x68531003 (Busy months)
• x68541102 (Busy events)
• x68511003 (Tentative months)
• x68521102 (Tentative events)
• x68551003 (Out of office months)
• x68561102 (Out of office events)
• x68470003 (Start of the published range)
• x68480003 (End of the published range)

All these properties live in the http://schemas.microsoft.com/mapi/proptag/ namespace.

We'll start with the last two properties. These contain the start date and the end date of the published data. These values always fall on month boundaries and are encoded in systime, a MAPI datatype.

You can use this code to convert a systime to a DateTime:

The other properties contain the actual free/busy data. For each free/busy status there are two properties: One describes the months which are covered, and one contains the availability data for those months. For example, the appointments marked as busy are recorded in the properties x68531003 and x68541102. The first property has a datatype of mv.int, the latter one is a mv.binary. Both arrays should have the same length, otherwise, the free/busy data is corrupted. To decode the values, you'll have to iterate through those arrays and decode the information. You can use this code snippet to do this:

The method requires you to extract the arrays from the xml response stream and decode the base64 encoded data to a byte array. The FreeBusyStatus type in line one is an enumeration consiting of the various free/busy status. The method iterates through the two arrays. From each entry in the monthValues array, it extracts the start date for that range. It then constructs a BinaryReader to read through the corresponding entry in the eventEntries array and extracts the event information from the stream. For each entry, the StoreFreeBusyEntry() is called to do something with the extracted information. In my library, I put them into a global list of events.

You'll have to call this method for each of the three pairs of properties. Note that not all properties are always set. If no appointment with a free/busy status of busy occurs during the published period, the two corresponding properties would be null.

This method will work with Exchange 2000 and 2003. It will also work with Exchange 2007 if you have the public folder tree installed, which is not longer mandatory.

When you create a meeting with OWA, it will display the availability information of the attendees like Outlook does. To get the information, it uses a special OWA command which returns the free/busy information as an XML stream.

Just issue this request to the server and you'll get your data:

The <startDate> and <endDate> must be replaced with the date range you are requesting, in the format yyyy-MM-ddTHH :mm:sszzz. An example would be 2004-01-01T14:00:00+02:00 (January first, 2004, two PM with a time-zone of two hours).
<interval> specifies the interval in minutes. Minimum is 5.
Finally, the <userEmail> must be replaced with the SMTP email address of the user for which the free/busy information is requested. If you want to request the free/busy data for multiple persons for the same date range, you can add more &u=SMTP:<Emailaddress>. However, the maximum length for the GET command is 1024 bytes.
The following example would request the free/busy data for John Doe (jdoe@contoso.com) for the 25 July 2004 from two PM to four PM CET (Central European Time, GMT+01:00) with an interval of 30 minutes:

The response will look like this:

Now, the interesting information is in the <a:fbdata> node. This node contains the requested data. Each digit represents one interval. The meaning is as follows:

• 0 equals CdoFree
• 1 equals CdoTentative
• 2 equals CdoBusy
• 3 equals CdoOutOfOffice

It is important that you send that User-Agent string along. If you don't pretend to be an Internet Explorer 6 or later, you won't get an XML response because OWA thinks you are using a down-level browser which don't understands XML.

This method will also not work with Exchange 2007, as most of the OWA commands have been removed from Exchange.

The Web Storage System of the Exchange system allows one to access the various properties of any item (e.g. a mail or appointment) via WebDAV.

To retrieve a list of all available properties, the WebDAV Propfind method is used, as displayed below:

However, this request will only return the named properties, such as the displayname, etc. The MAPI-Properties are not included in the list. Instead, the following request should be used, which uses the undocumented http://schemas.microsoft.com/exchange/allprop tag:

When a HTTP or WebDAV request is issued agains an Exchange 2003 or 2007 public folder or mailbox folder, the server returns a HTTP/1.1 440 Login Timeout error if Form Based authentication is enabled.

To work around this situation, you must do a logon to Outlook Web Access before performing any further requests. To do this, perform the following request against the exchange server:

Note: The url above is used with Exchange 2003. If want to authenticate against Exchange 2007 use this url:

The Exchange 2003 url is still there but it won't work.

Replace the<destination-url> with the url of the uri where you want to do your request. The<domain\username> and the <password> fields must be replaced with the credential you want to use during your session.

When the login was successful, you will receive two cookies that you must pass along with all further requests. If no cookies are returned, the logon was not successful.

C# Example

JavaScript Example

An often given solution to the problem outlined above is something like this (C#):

Now, the result variable contains all user-accounts with the given account name. But in a multi-domain environment, several users may have the same account name.
So, one must iterate through the list to determine the domain of each object. Unfortunately, that information is not stored within the user object.
Another drawback is, that the above solution can only be used from a computer which is logged on to a domain within the forest. From outside the forest, this will not work.
The solution in the next paragraph shows how to work around these issues.

To find an user-account object based on the domain\username information, follow the following steps:

1. Get the directory entry for RootDse (LDAP://RootDse or GC://RootDse).
2. From that entry, retrieve distinguished name for the configuration naming context (Property configurationNamingContext).
3. Get the directory entry CN=<domain name>, CN=Partitions, <distinguished name of configuration naming context>. Replace the <domain name> with the domain part of the username, and the <distinguished name of configuration naming context> with the distinguished name of the configuration naming context found above. If no such directory entry exists, the given domain was invalid.
4. From that entry, get the naming context of the domain (Property nCName).
5. Now that you have the distinguished name of the domain where the desired user account is located, you can do a search on that domain (depending on your environment and the required information from the user object, it may or may not be a good idea to use the global catalog).
   To find the user object in domain specified above, do a search with this filter: (&(objectCategory=person)(objectClass=user)(sAMAccountName=<username>)) (Replace the <username> with the name of the account you are searching for).
   This search will either return one found directory entry, or nothing if no user with the given account name exists.
   

C# Example