Migration << >>

Phased Migration Options

Your plan needs to include how many mailboxes will migrate to Microsoft Exchange Server at a time. Generally, migrating the entire postoffice (every mailbox) will be easier to plan for, implement and maintain than migrating a partial postoffice. Migrating a partial postoffice is more likely to occur during a pilot or limited rollout, when the number of users is small and the issues are easier to solve or work around. The following section explains why this is so.

Migrating a Partial Postoffice

When you migrate a partial postoffice, the MS Mail (PC) 10/10/10 (Network/Postoffice/Mailbox) address is not retained, which is a disadvantage for the following reasons:

Routing Change

No changes in the routing of e-mail from other postoffices and gateways are allowed when doing a partial postoffice migration. The mailboxes remaining on the postoffice need mail addressed to them to continue to be delivered.

MS Mail Gateway passthrough

Mail sent from external sources through Microsoft Mail (PC) gateways to the old address will be routed to the Microsoft Mail (PC) postoffice. This could cause mail to be returned as undeliverable or delivered to an unused mailbox.

To avoid this, you can update the gateway's mapping table (if there is one) so that mail is routed to the new address. For example, the Microsoft Mail (PC) X.400 gateway has an address mapping table so that mail addressed to the old X.400 address is redirected to the new MS type e-mail address of the Microsoft Exchange Server mailbox. Updating the mapping table works well during a pilot rollout, but isn't recommended when you're migrating thousands of mailboxes at once, because gateway performance will be affected.

Tip   Move users who send mail to each other frequently at the same time.

PABs for users who haven't migrated

Mail sent with old PAB addresses in Microsoft Mail (PC) will try to go to the old mailbox. If the mailbox has been deleted, the message will be returned as undeliverable. The sender can try to resend it using the Microsoft Mail (PC) global address list, which may or may not have been updated yet with the new address, depending on whether the directory synchronization cycle has completed. Users can synchronize their PAB with changes in the global address list using PABCheck.

Migrating an Entire Postoffice

If you migrate every mailbox on a postoffice at the same time, you can retain the original Microsoft Mail (PC) 10/10/10 (Network/Postoffice/Mailbox) addresses as their MS type e-mail addresses. This has many advantages, as follows.

PABs for users who haven't migrated

PAB entries function similarly to replies. For Microsoft Mail (PC) users, their PAB addresses continue to work for migrated mailboxes because the addresses are the same.

Migrated PAB entries will work for Microsoft Mail (PC) mailboxes that have not migrated. Mail addressed with the migrated PAB to mailboxes that have since migrated will get routed to the Microsoft Mail Connector. The Microsoft Mail Connector does not have a postoffice configured with that address and will return the mail as undeliverable. This undeliverable mail can be readdressed from the Microsoft Exchange Server global address list and delivered normally.

There is no tool that updates the user's PAB entries as changes are made in the Microsoft Exchange Server global address list. To prevent undeliverable mail, users can remove all PAB entries of MS type from their PAB after they are migrated to Microsoft Exchange Server mailboxes.