Top Tips when preparing for an Office 365 & Exchange Online migration

Here are my top tips when preparing for an on-premise to Exchange Online & Office 365 migration

  1.  Active Directory
    1. Identify Active Directory objects requiring remediation
    2. Install and run the Office 365 IDFix tool.  IdFix identifies errors such as duplicates and formatting problems in your directory before you synchronize to Office 365.
    3. Remediate any Active Directory objects identified by the IdFix tool
  2. User Principle Names (UPN’s)
    1. Identify the User Principle Name (UPN) of all accounts to be migrated that are not internet routable
    2. Office 365 requires that users have a valid, internet routable User Principal Name suffix, such as instead of contoso.local
    3. Change the User Principal Name on the accounts to be migrated to Office 365 to match the primary SMTP address
      1. Office 365 requires that users have a valid, internet routable User Principal Name suffix, such as instead of contoso.local.
      2. Email addresses are internet routable.
      3. Changing the UPN to the primary SMTP address solves many of the UPN validation problems like invalid characters, spaces, or even duplicate UPNs.
      4. Many times Office 365 services will ask for email address and password when it really wants a UPN.
  3. Large Items
    1. Mailboxes with items larger than 150MB cannot be migrated to Office 365.  Download and run one of numerous scripts to help identify mailboxes with items larger than 150MB
  4. Dynamic Distribution Groups
    1. Identify any Dynamic Distribution Groups.  These cannot be migrated to office 365.
    2. Summary of Problem
      1. When a mailbox is migrated from on-premise to Office 365, the mailbox no longer appears in the on-premise Dynamic Distribution Group
      2. Mailboxes in Office 365 cannot see on-premise Dynamic Distribution Group’s in the Global Address List (GAL)
    3. Summary of Solution
      1. Expand the filter on your Dynamic Distribution Lists to include “Users with external email addresses”.  This way , when the mailbox is migrated to Office 365 it will continue to appear in the Dynamic Distribution Group
      2. Create a contact in Exchange Online to represent the dynamic distribution group
      3. Exchange Online users can now select the dynamic distribution group from the global address list (GAL). When they do, messages will be delivered to the members of the group as defined by the settings for the group.
      4. Once all mailboxes are migrated recreate the dynamic distribution groups in Office 365
  5. Shared Mailboxes
    1. Identify any shared mailboxes and their delegates.   A shared mailbox and its delegates need to be migrated together
  6. Public Folders
    1. If your public folders are on Exchange 2010 or later servers, then you need to install the Client Access Server role (if not already installed) on all mailbox servers that have a public folder database. This allows the Microsoft Exchange RpcClientAccess service to be running, which allows for all clients (on-premise and O365) to access public folders
  7. Office 365 Tenancy
    1. Ensure you have the license and login details
    2. Verify if tenancy has been created
  8. Hybrid
    1. Provision a new public IP address on your firewall for your Hybrid environment
    2. Create an A record in your public DNS to represent your Hybrid environment pointing to this public IP address
  9. Unified Messaging (UM)
    1. UM needs to be disabled on a mailbox before it can be migrated to Office 365
    2. Office 365 can be enabled / configured for UM, but it requires a compatible telephony / voice system to be available to provide the dial tone.  This can be e.g. Lync / IP PBX.
    3. Verify that a compatible telephony / voice system to be available to provide the dial tone
  10. Journaling
    1. You can’t designate an Office 365 mailbox as a journaling mailbox. You can deliver journal reports to an on-premises archiving system or a third-party archiving service. If you’re running a hybrid deployment with your mailboxes split between on-premises servers and Office 365, you can designate an on-premises mailbox as the journaling mailbox for your Office 365 and on-premises ailboxes. Office 365 cannot host journaling mailboxes.
  11. Operating System
    1. Please ensure all clients who’s mailbox are being migrated are running the latest operating systems service packs
    2. Also, please review if you are likely to be in the following scenario.  If yes, you will need to implement the hotfix(es) (and registry entry) in the link below
      1. You have a third-party proxy server that enables communication only over port 80.
      2. You configure a computer that is running one of the following operating systems to use this proxy server for all protocols:
        1. Windows 8.1
        2. Windows Server 2012 R2
        3. Windows 7
        4. Windows Server 2008 R2
      3. You configure the proxy bypass list to contain settings for internal servers.
      4. You enable the Bypass proxy server for local addresses option.
      5. You configure Microsoft Outlook 2010 or Microsoft Outlook 2013 to connect to the newest Microsoft Office 365 mailbox (Wave15).
  12. Mail Routing
    1. Ensure that all outbound on-premise SMTP sending IP addresses are included in the inbound connector in Office 365.  E.g. if customer is using 2 separate firewalls outbound SMTP might go out on 2 public ip addresses – both addresses need to be included in the Office 365 inbound connector
  13. Firewall Rules
    1. Office 365 URLs and IP address ranges
      1. Ensure the following URL’s and IP addresses are accessible from computers on the network
    2. Exchange Online firewall requirements below.
      1. Office 365 to on-premise (Inbound to Hybrid Servers)
        1. Port 80/443 – (Exchange Online)
        2. Port 25 – (EOP IP address ranges)
      2. On-premise to Office 365 (Outbound from Hybrid  Servers)
        1. Port 80/443 – (Office 365 portal and identity and Exchange Online) *** If you have any Exchange 2010 CAS servers that are not Hybrid servers you will also need to allow them to communicate with Exchange Online. ***
        2. Port 25  – (EOP IP address ranges)

Best of luck!

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