How do I configure a Big Bang mailbox migration?

​​​​​​How do I configure a Big Bang mailbox migration?​


A single pass migration (Big Bang) strategy will move the entire mailbox in one pass, after MX records are cut over. A typical scenario consists in cutting over on a Friday evening and migrating during the weekend. 

This is useful when you want a cost-effective and simple migration strategy to implement. This is only really recommended for smaller migrations where you want to migrate everything in one pass.


MX Records Cutover:

MX records are used purely for email delivery by SMTP. The MX record for your domain points to the Source system, and after the MX cutover must point to the Destination system so that the email gets delivered to the new messaging system.

Changing MX records in DNS to point to the new system is not effective immediately, and is subject to replication delays. You will have to wait for the TTL (aka Time To Live) to expire; until then, email systems on the Internet may continue delivering to your old system.

  • Using this tool for your Source domain, you will find at what the TTL parameter is set to, so it will take those <TTL> hours to take effect.
  • To allow for faster switching of email delivery from Source to Destination, we recommend reducing the TTL value for the DNS record ahead of time. That way, when you cut over MX records in DNS to point to the Destination, the effect should be almost immediate.

Once MX changes replicate, new incoming email will be redirected to the new Destination system. At this point, your end-users should start working with their Destination mailboxes.

Migration may potentially not complete in time for various reasons:

  • Users accessing the new system may not have access to all their data when work resumes.
  • Any items created during or after the migration may be missed by a single pass.
  • Downtime may occur for some users if migration fails or takes too long.

To overcome this drawback, you would need to perform a multi-pass migration instead, by following one of the two strategies below:

Submit the Single Pass for Big Bang Migration:

There are three migration filters which you will have to properly adjust before submitting the Project because you will have only one opportunity:

  1. Date range filter in Edit Project -> Advanced Options.
  2. Folder filter (optional) in Edit Project -> Advanced Options.
  3. Selecting the types of data to migrate on the Start Migration panel.

Review carefully the migration filters to adjust them to the following:

Click on Edit Project -> Advanced Options -> Filtering tab, and set the earliest and latest dates from which to migrate.  Typically, for a Big Bang (single pass) migration you'll want to leave these checkboxes unchecked. By default, the system will not filter items by date unless the respective boxes are checked:

Set the folder filter if you want to select what folders should not be migrated:​


After reviewing migration filters, submit the single pass of a Big Bang migration for one or more mailboxes:

      1. Select one or more mailboxes already configured.
      2. Click on Start.
      3. Choose Full Migration.
      4. Ensure all of the types of data you wish to migrate are supported and selected.
      5. Select Start Migration (the license will be consumed only upon success).
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