This article describes Exchange Online and its innovative features. It's also a small migration guide.
 
We will describe this three points :
  • What is Exchange Online
  • New features in Exchange Online
  • Transitioning steps

1. What is Exchange Online :

 Unified communications is one technology trend that is seeing growth in nearly every business vertical. With an increased need for real-time communication and collaboration in order to stay competitive in business, organizations are turning to services such as Microsoft Exchange to improve anywhere access to key information, calendaring, and corporate communication.

Microsoft Exchange Online is designed for organisations who want to benefit from cloud-based email without sacrificing the business-class capabilities that Exchange Server has always provided. Built on the same technology as Exchange Server 2010, Exchange Online provides organisations with the latest capabilities including; built-in archiving, optional Conversation View, and MailTips, along with powerful web-based tools for managing online deployments. Microsoft handles the ongoing maintenance, patches and upgrades of the Exchange infrastructure while providing IT administrators the control and flexibility they require.

2. Features in Exchange Online :

  • Users will be able to send and receive messages up to 20MB including any attachments. In regards to client access, users can access their mailboxes via Microsoft Office Outlook 2007, Office Outlook Web Access, Microsoft Office Entourage 2008, and mobile device access (Windows mobile 6.0 devices, Nokia E and N series, Apple iPhone and BlackBerry).
  • Help protect your organization from spam and viruses with Microsoft Forefront Online Protection for Exchange, which includes multiple filters and virus-scanning engines.
  • Exchange databases in the Microsoft Online environment have been configured with a deleted item recovery time of 14 days and a deleted mailbox recovery time of 30 days. But please bear in mind that if you delete a mailbox you as an admin cannot reconnect it yourself. Instead you must submit a support request in order to have BPOS staff do it for you.
  • Work from almost anywhere and get automatically updated email, calendar, and contacts on the devices you use most, including PCs, Macintosh computers, iPhone, Android phones, Symbian phones, BlackBerry smartphones**, Windows Mobile, and Windows Phones*.
  • You can create Exchange users, groups, contacts, and conference rooms via the Microsoft Online Services Administration Center. You can also add senders to safe sender and blocked sender lists.
  • Service level agreement (SLA) for Exchange Online subscribers is 99.9% uptime. In case of disaster, Microsoft promises a recovery time objective (RTO) and recovery point objective (RPO) of 24 hours or less.
  • You can replicate users and migrate data from any Exchange 2000, 2003 or 2007 on-premise messaging infrastructure to Exchange Online. If you want to migrate from a legacy (such as Exchange 5.5) or foreign (such a Gmail, Yahoo, UW IMAP Server, Netscape, Sun One, Communicate Pro etc.) messaging environment to Exchange Online, the Exchange Online migration tools also have support for POP3/IMAPv4 based migrations, which would be used in such scenarios.

3. Transitionning steps :

 hen migrating from Exchange-based environments, you can establish directory synchronization so that AD users, groups and contacts are replicated to Exchange Online from your on-premise Active Directory environment. This will create a temporary unified GAL during the migration period. In addition, you will be able to share the same SMTP domain name between your on-premise messaging infrastructure and Exchange Online and thereby establish true e-mail coexistence.

Windows 2000, 2003 and 2008 Active Directories are supported by the Exchange Online migration tools.

Also, you do not necessarily need to migrate all your Exchange users, groups and contacts to Exchange Online, it is also supported to run in hybrid mode, where you migrate some of your users, groups and contacts to Exchange Online and keep the rest on-premise. If your business has a large and complex messaging infrastructure it is often a good idea to keep some Exchange servers in the on premise environment, as you probably have line of business applications that uses Exchange for relaying purposes, custom connectors to other systems etc.

Another thing worth mentioning is that you do not necessarily need to manage users, groups, and contacts that have been migrated to Exchange Online via the web-based Exchange Online services portal. Actually if you set up directory synchronization from your on-premise environment to Exchange Online, you must manage these objects via the Active Directory Users and Computers and Exchange Management Console MMC snap-ins or the Exchange Management Shell. Replicated objects cannot be managed via the Exchange Online services portal.

If you are establishing a greenfield, you can also create a brand new Exchange Online based messaging environment in which you manage Exchange objects via the Services portal.

Inbound e-mail from the Internet to Exchange users, groups and contacts hosted at Exchange Online is routed through Exchange Hosted Services. You can choose to have inbound mail point to your on-premising infrastructure or directly to Exchange Hosted Services, which routes it on to the respective Exchange 2007 server at Exchange Online.

Migration in one shot of less than 1,000 mailboxes from Exchange 2003, Exchange 2007 or Exchange 2010 :

Cutover Exchange Migration is the easiest way to provision cloud-based Exchange Online mailboxes and then migrate mailbox data to the cloud from your on-premises Exchange server. This option migrates your organization’s distribution groups, external contacts, email messages as well as other Exchange mailbox data such as calendar items, contacts and tasks. This allows you to migrate all of your mailboxes at once, such as over a weekend and is ideal for a small to medium sized organizations that desire less complexity and a short migration timeframe. You also do not need to install and configure the Microsoft Online Services Directory Synchronization tool or DirSync in this instance; this option is ideal if you plan on identity management entirely in the cloud. Please note that this method should not be used if you plan to maintain any mailboxes on-premises after the migration.

Migrating mailboxes from Exchange 2003 or Exchange 2007 and you have one of these cases:

- Maintain mailboxes in your on-premises organization
- H
ave more than 1,000 mailboxes to migrate
- H
ave requirements to pilot or stage migrations
- Do not require calendar free/busy sharing between cloud and on-premises users

In these cases, staged Exchange Migration may be the best option for you. This option allows your organization to move some mailboxes to the cloud over time while maintaining the rest of your mailboxes in your on-premises environment so you can migrate your mailboxes in discrete batches. You get a unified global address list for both your on-premises and cloud-based mailboxes but need to replicate user objects from your on-premises Active Directory directory service to your Office 365 environment to do so; this means you will need to install and configure the Microsoft Online Services Directory Synchronization tool and keep on managing user attributes in your on-premises Active Directory. For more information, see Plan for User Identity in a Staged Exchange Migration.

Migrating mailboxes from Exchange 2003, Exchange 2007, 2010 and you have one of these cases :

- You need to maintain mailboxes both in the cloud and in your on-premises organization indefinitely
You need to migrate all mailboxes to the cloud but have a requirement to pilot or stage migrations of mailboxes over an extended period of time
-
Have a requirement to have the smoothest possible migration experience including free/busy calendar sharing between cloud and on-premises users, have a single Outlook Web
App URL for both on-premises and cloud users
- You want
 centralize control of mail flow so your on-premises organization can control mail flow for both the on-premises and cloud-based organizations?

In this case, a Hybrid deployment is likely the best option for your organization. This enables seamless calendaring between hosted and on-premises users and all email looks and feels internal to the company; recipients on email are resolved as internal, MailTips will work correctly and OOF messages to internal recipients will apply to both on-premises and Exchange Online cloud-based user mailboxes. Human resources teams or your compliance officers can conduct multi-mailbox searches/discovery across both on-premises and Exchange Online mailboxes. You can even move mailboxes back to on-premises if requirements or scenarios change and users’ Outlook profile is preserved so users do not need to resynchronize or create new .OST files.

In the hybrid scenario, an Exchange 2010 SP1 (or higher) server must be deployed on-premises which acts as a gateway to the cloud; larger organizations will typically deploy two of these servers for redundancy. There is no need to upgrade mailboxes to Exchange 2010 prior to moving them to the cloud if you are currently running Exchange 2003 or Exchange 2007. You can migrate and manage on-prem and online users from the same Exchange Management Console or using Remote PowerShell. Setting up a hybrid deployment has more steps to consider than the other options but provides the most flexibility, particularly if your organization intends to maintain mailboxes on-premises and in the cloud for an extended period of time.

Note: Currently, you cannot migrate directly from Lotus Domino to Exchange Online. You must first migrate Lotus Domino to an on-premise Exchange environment using the Microsoft Transporter Suite and then migrate from there to Exchange Online. Alternatively, you must migrate from Lotus Domino using a POP3 or IMAPv4 based migration approach. But Quest Software should be working on a solution that will make it possible to migrate directly from Lotus Domino to Exchange Online.

Ref :

http://community.office365.com/en-us/b/microsoft_office_365_blog/archive/2011/09/01/migrating-to-exchange-online-in-office-365-for-enterprises.aspx