Ask the Expert

Feasibility of long-term Exchange 5.5 and Exchange 2003 coexistence

My company has proposed a plan where our Exchange 5.5 will coexist with Exchange 2003 for one year. This implies a progressive migration of every user, replication between the two environments of the information in the global address list, replication of users between every Exchange server, etc.

Many experts say that this is not recommended, and that we should migrate on a short period, and not coexist for so much time. In spite of expert advice, our IT manager absolutely wants a coexistence plan. Up until now, we have had many problems with this kind of migration.

What is your opinion about this approach to migration?

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Long term coexistence always lends itself to particularly careful planning and the ability to consider third-party tools. I've always believed that the third-party market is particularly useful when you are considering these long term inter-org coexistence models. Without it, you will be dependent on tools that were more likely designed for shorter migration periods.

You will most likely need a solution for: a unified global address list, distribution list synchronization, public folder data/permission/forms/views synchronization, etc. In addition, you need to factor in the overhead of additional support for two production systems.

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Related information from

  • Reference Center: Replication and synchronization
  • Learning Guide: Exchange migration
  • Reference Center: Migration advice

  • This was first published in September 2005

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