Autodiscover flow in an exchange hybrid environment part 1#3 part 32#36

of 26 | Autodiscover flow in an Exchange Hybrid environment | Part 1#3 | Part
32#36
Written by Eyal Doron | o365info.com | Copyright © 2012-2015
Autodiscover flow in an Exchange
Hybrid environment | Part 1#3 | Part
32#36
The Autodiscover flow in an Exchange Hybrid based environment, can be
considered the most complex flow because the Autodiscover “journey” is
implemented in two different environments.
Regarding users whom their mailbox was migrated to the “cloud” (Exchange
Online), the Autodiscover journey will start by the Autodiscover client by addressing
the Exchange on-Premises infrastructure.
Autodiscover flow in an Exchange Hybrid environment | The article
series
The first article is the first article on a series of three articles and the main focus is -
presenting the logic and, the involved components in the Autodiscover flow that is
implemented in Exchange Hybrid environment.

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In the next two articles, we will review the Autodiscover flow that is implemented in
Exchange Hybrid environment by using the Microsoft web-based tool, the Microsoft
Remote Connectivity Analyzer (ExRCA).
 Autodiscover flow in an Exchange Hybrid environment | Part 2#3 | Part
33#36
 Autodiscover flow in an Exchange Hybrid environment | Part 3#3 | Part
34#36
Note – you can read more information about how to use the Microsoft Remote
Connectivity Analyzer (ExRCA) tool in the article – Microsoft Remote Connectivity
Analyzer (ExRCA) | Autodiscover troubleshooting tools | Part 2#4 | Part 22#36
Current article and the next articles
The current article serves as a high-level review of the Autodiscover flow in
Exchange Hybrid environment.
The “Autodiscover flow” is based on a scenario in which the Exchange on-Premises
user mailbox was migrated to the “cloud” (Exchange Online).
The user which try to create a new Outlook mail profile be address by default the
Exchange on-Premises infrastructure and because the user mailbox is a “cloud”
mailbox, the Exchange on-Premises server will send the recipient information about
his “cloud E-mail address”.
The Outlook client will start the Autodiscover process by using the “cloud” E-mail
address.
In the next articles in this article series, we will “watch closely” the Autodiscover flow
by using the ExRCA tool and, analyze each of the different phases that are involved
in the process.

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The Autodiscover client
The term “Autodiscover client”, describe the element that needs to retrieve the
Autodiscover information from the Autodiscover Endpoint (Exchange server).
In the Exchange Hybrid environment, we can point to the type of Autodiscover
clients:
1. Exchange mail client
The Autodiscover process that is implemented by the Exchange client that needs
access to their mailbox.
The Autodiscover client could be any type of mail client such as- Outlook, mobile
device (ActiveSync client) and so on.
2. Server to server
The other type of Autodiscover client could be another Exchange server.

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In the Hybrid environment, the Exchange On-Premise infrastructure and the
Exchange Online infrastructure operates as one logic entity.
When relating to the subject of Exchange web service, the information is shared
between the two different Exchange infrastructures (Exchange on-Premises and
Exchange Online (by Relies on the Autodiscover infrastructure.
When Exchange Online infrastructure needs to get information about a specific
Exchange on-Premises recipient, Exchange Online will locate the Exchange on-
Premises server by using the Autodiscover process.
For example, when a “cloud user” (user who has an Exchange Online mailbox) need
to see Free/Busy time of Exchange On-Premise user (user that his mailbox is hosted
on the Exchange On-Premise server), the request for the information will be sent
from the Exchange Online server to the Exchange On-Premise server.
The Exchange Online “find” or “allocate” the Exchange On-Premise server by using
the Autodiscover services.
Exchange On-Premise and Exchange Online – Best
friends forever
The infrastructure of Hybrid environment is very sophisticated and compound and,
the Autodiscover infrastructure are only a part of this infrastructure.
In this article, we will relate only to the subject of Autodiscover in Hybrid
environment and not to the “other parts” of the Hybrid environment but, it’s very
important to understand that the Autodiscover serves as an infrastructure for many

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other parts of the Hybrid environment such as – Free/Busy time, Mail tips, out of
office, move mailbox (mail migration) and so on.
Hybrid environment different environment and Exchange client
Transparency
The beautiful part in the Hybrid environment is, that although the Hybrid
environment is connecting two entirely deferent environment – Exchange On-
Premise and Exchange Online environment (and if we want to add more complexity
to the description a relationship between the On-Premise Active Directory and the

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Windows Azure Active Directory) and, despite that fact that the term “Hybrid
environment” is composed of many different parts, from the Exchange client’s point
of view, this compound infrastructure is “unnoticeable”.
For example, in an Exchange hybrid environment, a recipient named “Alice” wonder
if she is hosted at the Exchange Online or Exchange On-Premise, for Alice, there is
no way to get this information.
My point is that as Exchange administrator in Hybrid environment we have to be
familiar with the “inside infrastructure of the Hybrid environment and the
Autodiscover process” but, the advantage is that from the user point view this
infrastructure (the Hybrid environment) is transparent.
Hybrid environment and SMTP domain name space
Exchange hybrid environment was created for “combing” to different
infrastructures into one logical entity.

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In Exchange Hybrid environment, the organization user’s mailboxes are “spread”
between two different environments – the organization environment (Exchange on-
Premises) and the cloud environment (Exchange Online).
The organization users are not aware to this two different infrastructure but in
reality, we are dealing with two totally different environments.
The “magic glow” that sticks together this two different infrastructure is
implemented by implementing Exchange organization relationships between the
two different infrastructures.
Each of the “physical infrastructure” – Exchange on-Premises and Exchange Online
needs to relate to the “other” Exchange infrastructure by using a different domain
namespace (SMTP domain name space).
 The Exchange Online environment, relate to objects that are physically
located at the Exchange on-Premises environment by using the “public
domain name”.
 The Exchange on-Premises environment, relate to objects that are physically
located at the Exchange Online environment by using the “Hybrid domain
namespace”.

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The ability of Exchange infrastructure to “hide” the complex in from the Exchange
client is implemented by “Juggling with the SMTP domain namespaces”.

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The relationships between the recipient E-mail address and the
Autodiscover process
In the next section, we will review that subject of the different SMTP domain
namespace in the Exchange hybrid environment.
Apparently, there is no clear relationship between the subject of E-mail address and
the Autodiscover process, but in reality, in the Exchange hybrid environment, the
Autodiscover flow is fully relying on the user E-mail address.

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In Exchange hybrid most of the time the “Autodiscover focal point” is the Exchange
on-Premises environment.
As mentioned, organization users don’t really know where is their Exchange
mailbox is located.
In a scenario in which user mailbox is located at the Exchange Online infrastructure,
the organization user will start the Autodiscover journey by addressing the
Exchange on-Premises infrastructure and the Exchange on-Premises will notify him,
that he needs to restart the Autodiscover journey by addressing different Exchange
infrastructure – the Exchange Online infrastructure.

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The SMTP domain name spaces in an Exchange hybrid
environment
In Exchange Hybrid, there is a minimum of a three domain name space. The
Exchange hybrid environment is using two domain namespaces and the third
domain namespace “belong” to the Office 365 infrastructure.
1. Public domain name (public SMTP domain name)
This public domain name is the “formal” organization domain name that is used by
the Exchange On-Premise infrastructure and in a scenario of Hybrid environment,
the public domain name is used also, for “representing” cloud recipient.
Exchange on-Premises recipient and the Exchange Online recipient will continue to
use an E-mail address that uses the “public domain name”.
For example, in a scenario in which the public domain name is o365info.com all the
organization recipients whom their mailbox is located at Exchange on-Premises and
the organization user whom their mailbox is located on Exchange Online will
continue to use the specific domain name.
This public domain name described as – “shared domain name” because it is shared
between two different Exchange Online infrastructures (Exchange on-Premises
versus the Exchange Online infrastructure).
2. Office 365 Tenant built-in domain namespaces

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When we open a new Office 365 subscription, we are required to provide an
“organization name”.
In our scenario, the Office 365 tenant domain name is – 365info2
After we provide the required organization name, Office 365 start an automatic
process in which it creates two new “Office 365 tenant domain names”.
Based on the Office 365 tenant domain name, the following two domain names are
created.
1. onmicrosoft.com
2. mail.onmicrosoft.com
Onmicorosft domain name | The default tenant domain name
The second domain name could be described as the “default Office 365 tenant
domain name”. This domain namespace is not used by the Exchange hybrid
environment.
In case that the organization name who was registered at Office 365 is – 365info2,
this name will be “attached” to the office 365 default domain name
– onmicrosoft.com and, the result is a domain name that represents the specific
Office 365 tenant. In our scenario –365info2.onmicrosoft.com
The 365info2.onmicrosoft.com domain namespace is used only by the Office 365 and
Exchange Online environment.
Q: What is the reason for this “default Office 365 domain name”?
A: There are two main reasons:

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The need for using a “dedicated domain namespace” such
as 365info2.onmicrosoft.com was created for two main reasons –
Reason 1 – Each “entity” in Office 365 must have a UPN name who includes a
domain name suffix and each of the Exchange Online entities (such as recipient)
must have an E-mail address that includes a domain name suffix.
When we create the Office 365 tenant, the Exchange Hybrid still does not exist or is
not yet defined and the Office 365 infrastructure needs some kind of “identity” for
the Office 365 objects such as users.
Chronologically, Office 365 “doesn’t know if we are going to build and implement an
Exchange Hybrid environment.
Reason 2 – Office 365 infrastructure can “host” a local object (users, mailboxes, etc.)
that doesn’t relate in any way to the Exchange Hybrid infrastructure.
In case that we create such object, for example, a “cloud user” that is not
synchronized from the On-Premise Active Directory, this object needs to have an
identity.
Onmicorosft domain name | “Hybrid domain namespace”
The third “Office 365 domain name” that is created by default could be described as
the “Exchange Hybrid domain namespace”.
This specific domain namespace will be used only in Exchange hybrid scenarios.
The structure of the “Hybrid domain namespace” is based on the following formula
–
<Office 365 organization name> + <mail> + < onmicrosoft.com>
In case that the organization name that was registered at Office 365 is – 365info2,
this name will be “attached” to the “mail” domain name + the office 365 default
domain name –onmicrosoft.com and, the result is the Exchange hybrid domain
name –365info2.mail.onmicrosoft.com

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The Exchange Hybrid domain namespace is used by the Exchange on-Premises
infrastructure for routing purposes.
The “routing” is related to two different infrastructures
1. Mail flow
Each time that Exchange On-Premise server recipient needs to send E-mail
message to the Exchange Online recipient, the request will be accepted by the
Exchange on-Premises that “understand” that the destination recipient is located at
the Exchange Online infrastructure.
The Exchange on-Premises will use the “Hybrid domain namespace” of the
destination recipient. In Exchange Hybrid the each of the mail message that are
sent to the Exchange “Hybrid domain namespace” will be routed to the Exchange
Online server.
2. Autodiscover flow
The use of “Hybrid domain namespace” is related also to the Autodiscover flow in
an Exchange Hybrid environment.
When a user whom his mailbox is located at the Exchange Online infrastructure, try
to get Autodiscover information, he will address the Exchange on-Premises server.
When the Exchange on-Premises server “notice” that the recipient considers as an
Exchange Online recipient, the Exchange on-Premises send as a reply the E-mail
address that includes the “Hybrid domain namespace”. In our scenario
– 365info2.mail.onmicrosoft.com
When the Autodiscover client gets this information, he “understand” that he needs
to create a new Autodiscover process, but now, address the Autodiscover Endpoint
that is responsible for the domain name – 365info2.mail.onmicrosoft.com

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In the following diagram, we can see the logic structure of the SMTP domain name
in Hybrid environment.
Hybrid environment | recipients and their E-mail address
To demonstrate to the concept of multiple E-mail addresses in the Hybrid
environment, let’s use the following scenario:
Alice is a corporate employee whom her mailbox was “relocated” (moved) to the
cloud (Exchange Online).
In the Exchange On-Premise server, Alice is configured as a Remote mailbox.
The Exchange On-Premise “know” that Alice has two E-mail address: the standard
public E-mail address – Alice@o365info.com and additionally, the “Hybrid
environment service domain E-mail address – Alice@o365info2.mail.onmicrosoft.com
In Office 365 and Exchange Online, Alice will have the same two E-mail addresses
and additional E-mail address – Alice@o365info2.onmicrosoft.com
The “additional E-mail address”, the E-mail address (the E-mail address without the
“subdomain: mail) is based on the “Office 365 SMTP domain name” that is
automatically allocated to each of Office 365 users who have a mailbox.

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To demonstrate the difference between the Exchange On-Premise environment
and the Exchange Online environment, let’s take a look at Alice’s mailbox
proprieties.
In the following screenshot, we can see Alice’s mailbox proprieties in Exchange On-
Premise.
As we can see, Exchange On-Premise “know” about two E-mail address that Alice
has.
The E-mail address – Alice@o365info2.mail.onmicrosoft.com is based on the SMTP
domain name that we call “service domain name” in Hybrid environment.
Exchange on-Premises refers to the “Exchange Online E-mail address” as –
Routing E-mail address.

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Exchange 2013 server interface

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In the next screenshot, we can see Alice’s mailbox proprieties in Exchange Online.
As we can see, the Exchange Online “know” about three E-mail address that Alice
has.
The “additional E-mail address” that Alice has is – Alice@o365info2.onmicrosoft.com

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Why are you telling me all of this information?
In case that you’re wondering – “how does this information relate to me”?
The answer is that we need to understand the Hybrid environment infrastructure
such as the subject of E-mail address and the multiple SMTP domain name spaces,
so we will be able to understand better the Autodiscover workflow in a Hybrid
environment.

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Hybrid environment | Exchange on-Premises recipient
versus Exchange Online recipient the Autodiscover flow
In Hybrid environment, the user organization user’s mailbox can be hosted on the
Exchange on-Premises infrastructure or the Exchange Online infrastructure.
The main difference between the Autodiscover flow for Exchange on-Premises
recipient versus, Exchange Online recipient is that for Exchange on-Premises
recipient, the Autodiscover Endpoint is the Exchange on-Premises server.
Regarding recipients that their mailbox is hosted at Exchange Online, the Exchange
on-Premises serve just as an element that will serve for routing Autodiscover client
request to the Office 365 Autodiscover infrastructure.
For recipients whom their mailbox is located at the Exchange on-Premises, the
Autodiscover flow is implemented in the following way:
1. The Autodiscover will access the local On-Premise Active Directory (using an
LDAP query), asking for a list of Exchange On-Premise servers that can provide
him the required Autodiscover information.

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2. The Autodiscover client will connect local DNS server, asking to resolve the host’s
names of the local Exchange On-Premise servers that was returned by the On-
Premise Active Directory.
3. The Autodiscover client will try to connect the Exchange On-Premise server
Regarding the Autodiscover flow in an Exchange hybrid environment, for recipients
whom their mailbox is hosted at Exchange Online, the Autodiscover flow is a little
be more complicated and involved additional steps.
For recipients whom their mailbox is located at the Exchange Online, the
Autodiscover flow is implemented in the following way:

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1. The Autodiscover will access the local On-Premise Active Directory (using an
LDAP query), asking for a list of Exchange On-Premise servers that can provide
him the required Autodiscover information.
2. The Autodiscover client will connect local DNS server, asking to resolve the host’s
names of the local Exchange On-Premise servers that was returned by the On-
Premise Active Directory.
3. The Autodiscover client will try to connect the Exchange On-Premise server.
4. The Exchange On-Premise response with a “redirection message” informing the
recipient that for getting the required Autodiscover services, he will need to use
a different E-mail address, his Office 365 tenant E-mail.
5. Exchange client will start the Autodiscover process all over but now, by
addressing the Exchange Online infrastructure.
To demonstrate the process of Autodiscover flow in the Hybrid environment, for a
recipient that his mailbox is hosted in the cloud (Exchange Online), Let’s use the
following scenario:
 Alice’s mailbox is hosted at Exchange Online (the Exchange infrastructure is
based on Hybrid environment).

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 Alice needs to create a new Outlook mail profile, so she will be able to connect
to her mailbox (Exchange Online mailbox).
 The Exchange on-Premises relate to Alice’s mailbox as a “remote mailbox”.
Step 1 – Locating Autodiscover Endpoint in Active Directory-based
environment.
I in a scenario of the remote mailbox (cloud mailbox) the first part of the
Autodiscover flow is identical to the Autodiscover flow that is implemented by a
recipient who has a “standard mailbox” on the Exchange On-Premise server.
When Alice tries to create a new Outlook mail profile, Outlook will query the local
On-Premise Active Directory for the names of Exchange On-Premise servers who
provide the required Autodiscover services.
Outlook will locate an optional Exchange On-Premise server and ask him for the
required Autodiscover information.

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Step 2 – Addressing the Exchange on-Premises server
Technically speaking, Exchange server doesn’t know who “Alice” is. To be able to get
a detailed information about Alice, Exchange on-Premises contacts the local On-
Premise Active Directory asking for information about Alice.
The answer from the On-Premise Active Directory, include information about the
fact that Alice’s mailbox is a “Remote mailbox” and Alice have the following Routing
E-mail Address – Alice@o365info2.onmicrosoft.com

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Step 3 – Autodiscover client starts the Autodiscover flow by addressing
Exchange Online infrastructure.
The Autodiscover client will start a new DNS query looking for a host named –
o365info2.onmicrosoft.com
Note – in most of the scenarios, this name will not be resolved but instead, only the
hostname –Autodiscover.o365info2.onmicrosoft.com

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Step 4 – verifying if the Autodiscover Endpoint can communicate using HTTPS.
The Autodiscover client will try to create an HTTPS session to the “destination
Autodiscover Endpoint” (Exchange Online) asking for the required Autodiscover
services.
The next articles in the current three articles series are:
 Autodiscover flow in an Office 365 environment | Part 2#3 | Part 30#36
 Autodiscover flow in an Office 365 environment | Part 3#3 | Part 31#36
In this articles, we will use the ExRCA tool for providing a detailed review the
Autodiscover flow in Hybrid environment
Additional reading
 Office 365 Insight into the Hybrid Configuration Wizard Part 2

Autodiscover flow in an exchange hybrid environment part 1#3 part 32#36

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