Maintaining Distribution Lists

During multi-phase migration, when lists and addresses are changing, you can ensure correct routing to distribution list members by using one or more of the following methods:

• Migrate distribution lists to Microsoft Exchange Server before moving the mailboxes. (This may be the best choice, because custom recipients are automatically converted to mailboxes.)
• Set up a forwarding scheme.
• Convert distribution lists to public folders.
• Maintain duplicate lists on both systems.
• Disable distribution lists until migration is complete.
• Update the existing lists frequently.

Note   Most source extractors do not migrate distribution lists. See the appropriate chapter for information about your source extractor.

Throughout this guide, the term existing system refers to the messaging system you are migrating from.

Moving Distribution Lists

After gateways and directory synchronization processes between your existing system and Microsoft Exchange Server are working properly, you can move distribution lists.

The following figure shows a distribution list during early migration. As users are moved, the Migration Wizard replaces custom recipient addresses with new Microsoft Exchange Server addresses.

The next figure shows the same distribution list during later migration.

The Migration Wizard can only update distribution lists in the same site in which the custom recipients are created. For this process to work smoothly, create all first-level distribution lists, such as teams or workgroups, in the site where the custom recipients and mailboxes for those teams are created. Higher-level distribution lists, such as for company divisions, are composed of first-level distribution lists. Therefore, they can be created in the central site, because they have no custom recipients or mailboxes as members.

Setting Up a Forwarding Scheme

Instead of maintaining distribution lists during migration, you can preserve the existing distribution lists and mailboxes until your move is complete. Then you configure the existing system to forward all mail to the new Microsoft Exchange Server mailboxes.

Benefits and Limitations

The benefits of this method are:

• Maintenance is not required during migration.
• You can solve problems related to gateway pass-through, replies to sent mail, and personal address books.

The limitations of this method are:

• You have to re-create the distribution lists on Microsoft Exchange Server when your move is complete.
• Messages sent from Microsoft Exchange Server to distribution lists with members on Microsoft Exchange Server cross the connection twice.
• Messages are forwarded individually, leading to multiple copies in Microsoft Exchange Server.

Converting Distribution Lists to Public Folders

You can use public folders to replace distribution lists, so that users can view a history of recent messages in a public folder. To move users from distribution lists to public folders, perform the following steps:

1. Create public folders that correspond to distribution lists on your existing system.
2. Add a rule on each public folder to forward all new items to all members of the distribution list who have mailboxes that have not been migrated to Microsoft Exchange Server.
3. Give user permissions on a public folder to all Microsoft Exchange Server members of the corresponding distribution list.
4. After the name of a public folder is visible in the existing system, remove the corresponding distribution list.

Benefits and Limitations

The benefits of this method are:

• New users see a history of recent mail.
• The transition to public folders is part of migration.

The limitations of this method are:

• All the rules and permission maintenance must be done from Microsoft Outlook; changes aren't made automatically.
• Mail sent to the public folder from the existing system crosses the gateway twice to reach members on the existing system.

Maintaining Duplicate Distribution Lists

To keep network traffic to a minimum, you can have copies of the distribution list on both the existing system and Microsoft Exchange Server. Distribution lists are excluded from directory synchronization between the two systems to avoid duplicate names in the address lists. Only the Microsoft Exchange Server distribution lists appear in its address list, and only the existing system's distribution lists appear in its directory. This method works well if you use an automated process to modify distribution lists.

Benefits and Limitations

The benefits of this method are:

• Custom recipients are updated automatically in the Microsoft Exchange Server distribution lists, with the same rules and exceptions.
• When migration is finished, the complete distribution list is already on Microsoft Exchange Server.
• Mail sent to the Microsoft Exchange Server distribution list is handled by Microsoft Exchange Server, so only one copy of each message is delivered to each messaging system.

The limitations of this method are:

• Your existing system may lack distribution list features.
• Maintaining duplicate lists can require more effort than maintaining one distribution list on one system.

Disabling Distribution Lists

You can save the list of distribution list members and then delete or disable all distribution lists. After migration is complete, you create the distribution lists on Microsoft Exchange Server with new addresses. This requires no maintenance during migration but may disrupt normal e-mail traffic.

Benefits and Limitations

The benefits of this method are:

• Fewer resources are needed during migration.
• No maintenance is required during migration.

The limitation of this method is:

• Some groups may have a critical need for distribution lists and cannot wait for a slow, multi-phase migration to be completed.

Updating Distribution Lists

You can keep distribution lists on the existing system and update them after each phase of migration. This works well if you use an automated process of modifying the distribution list to include new addresses and to remove the old addresses.

Benefits and Limitations

The benefit of this method is:

• Less effort is required before migration.

The limitations of this method are:

• Your existing system may lack distribution list features.
• You have to re-create all the Microsoft Exchange Server distribution lists at the end of migration.