What is coexistence?

Coexistence is a migration path:

  • that takes some time to complete;
  • where a same mail domain name will be used by two mail systems at the same time;
  • where migrated and non-migrated users must be able to send mails to each other and reply to mails, and also share a same address book, reserve resources, etc.


As you know, mails can be delivered only in one place (because DNS MX records are pointing to one mail system).

  • The approach you will use will be to keep the mail routing as is.
  • You will not modify your MX records (they will remain pointing to the source).
  • You will also attach this domain name in the new target system.
  • Since MX records will not be pointing to the target, mails coming from the internet will still be arriving at the source.


If you are planning to run your migration over a few months, coexistence is the right way to go.
Setting up coexistence involves:

  • synchronizing address books; and,
  • setting up forwarders to deliver mails properly.

Cloudiway migration benefits

  • Cloudiway migration is synchronizing your users, groups and contacts, is provisioning users and is assigning licenses.
  •  Your address books remain synchronized during migration.
  •  User passwords can also be synchronized during migration.
  •  You can migrate your users in batches. Using Cloudiway migration, you will be able to provision and migrate the users in each batch at a time and date of your choice.

Putting in place delivery and forwarders is not performed by the platform. You must put it in place manually (through scripts). Usually, it involves activating a forwarder at the mail relay level, or in Exchange servers.

Example for setting up forwarders:
Create a forwarder in Exchange 
Create a forwarder in Office 365