More About Coexistence and Migration

We already blogged about coexistence and migration. But because we received so many questions about how coexistence might actually work, we thought we’d clarify in a new post.

Suppose that your users have email addresses such as user@company.com, but should be migrated to BPOS or hosted Exchange. You may want to move users one group at a time. Because you’re paying for a new email system, you also want migrated users to be able to fully utilize their new mailbox as quickly as possible. In other terms you want coexistence: for the time being, some users will use their old mailbox, while others should be able to use their new mailbox.

Here is the procedure which we found works best (here BPOS is just taken as an example):

• In BPOS, create a primary (user@company.com) and secondary (user@mso.company.com) email address
• In your original email system, leave the MX record untouched
• In your original email system, forward emails from the primary (user@company.com) to the secondary (user@mso.company.com)
• In BPOS, users can login as user@company.com and continue to send/receive emails without any disruption.

Of course, there are a few limitations you should be aware of:

• Free/busy information may not be synchronized across email systems
• Mailbox delegate access may stop working between email systems
• Email delivery may be delayed because of email forwarding
• Etc.

While this solution is not perfect, we found that it usually works very well. Do not hesitate to contact us if you have any questions: we’d be more than happy to help.