DAC means Datacenter Activation Coordination, that is used in Exchange 2010 to determine whether the database availability group is allowed to mount a mailbox databox in mailbox server or not. This activation is controlled by a bit stored in each DAG member memory; a bit set by the Datacenter Activation Coordination Protocol (DACP).

The Mailbox Transport Submission and Mailbox Transport Delivery services are used to provide separate mail submission and delivery processes.

The basic submission process works like this:

• The Mailbox Transport Submission service receives SMTP messages from the Transport service on the local Mailbox server or on other Mailbox servers.
• The Mailbox Transport Submission service connects to the local mailbox database.
• The Mailbox Transport Submission service uses RPC to deliver the message.

The basic delivery process works like this:

• The Mailbox Transport Delivery service connects to the local mailbox database using RPC to retrieve messages.
• The Mailbox Transport Delivery service submits messages over SMTP to the Transport service on the local Mailbox server or on other Mailbox servers.
• The Transport service routes messages using SMTP.

Its a mail routing service that handles mail flow, routing, and delivery within the Exchange organization.

This service processes all mail that is sent inside the organization before it is delivered to a mailbox in the organization or routed to users outside the organization.

Processing ensures that senders and recipients are resolved and filtered as appropriate, content is filtered and has its format converted if necessary, and attachments are screened.

• First we create a batch migration request for the mailboxes that we want to move using either Exchange Admin Center or Exchange Management Shell.
• The request is sent to the Mailbox Replication Service running on a Client Access server in the current Active Directory site. This server acts as the Mailbox Replication Service proxy.
• MRS adds the mailboxes to the Request queue and assigns the status Created to the request. This indicates the move has been requested but not started. 4) When a request is at the top of the queue, MRS begins replicating the related mailboxes to the destination database and assigns the Syncing status to the request.
• When MRS finishes its initial replication of the mailboxes, the service assigns the Synced status to the request.
• The request remains in the Synced state until you or another administrator specifies that you want to complete the request. MRS performs a final data synchronization and then marks the request as Completed.
• When the request is completed, the mailboxes are available in the new location. Because users can continue to access their email accounts during the move, you can perform online moves and migrations at any time.

When moving Exchange 2007 or Exchange 2010 installations to Exchange Server 2013, you cannot perform an in-place upgrade. Instead, you must install new Exchange Server 2013 servers into the existing organization and then migrate to Exchange Server 2013.

These are the steps are involved in migrations :

• Plan to migrate all Exchange servers in a particular site to Exchange 2013 at the same time. You should start with Internet-accessible Active Directory sites and then migrate internal Active Directory sites. For each Exchange 2013 Client Access server, you can configure only one Outlook Web App URL for redirection.
• If you plan to have a legacy Edge Transport server in your Exchange 2013 organization, install it prior to installing Exchange 2013 on any server in your organization.
• Install Exchange Server 2013 on new hardware and make it a member of the appropriate domain in the forest. You should install the Mailbox Server role first and then the Client Access Server role. You can install these roles on a single server or on multiple servers. You must deploy a Client Access server in each Active Directory site that has a Mailbox server.
• Move Internet mail flow from Exchange 2007 or Exchange 2010 to Exchange 2013.
• Move mailboxes and public folders from the existing Exchange 2007 or Exchange 2010 installations to the new Exchange Server 2013 Mailbox server or servers. If you move a mailbox that is part of an email address policy, the email address for the mailbox is automatically updated based on the settings in the email address policy. In this case, the new email address becomes the primary address, and the old email address becomes the secondary address.
• During a migration, the version of a CAS feature that a user sees, such as Outlook Web App, depends on where the user’s mailbox is located. If the mailbox is on an Exchange 2007 server, the user sees Exchange 2007 versions of CAS features. When you move the mailbox to Exchange 2013, the user will see Exchange 2013 versions of CAS features.
• Once you’ve complete the move and have validated the configuration, you can remove unneeded Exchange 2007 or Exchange 2010 servers from the organization.