This KB article contains information that may be useful for providers performing transition from Exchange 2010/2013 to Exchange 2016.
How to delay mailbox migration to wait until DNS changes are propagated
When an Exchange subscription is migrated from Exchange 2010/2013 to Exchange 2016, its Exchange DNS records are updated correspondingly on DNS servers managed by Odin Automation. Since DNS changes are not propagated immediately, the Exchange DNS records may point to Exchange 2010/2013 servers even though the Exchange subscription and its mailboxes have been migrated. As a result, the mailbox users will be unable to access their mailboxes through Outlook using Autodiscover until the corresponding DNS changes are propagated (Outlook relies on Exchange Autodiscover CNAME DNS records to access mailboxes). To prevent this issue, you can set a delay between updating Exchange DNS records and migrating mailboxes (see the instruction in the internal part of the KB article). We recommend that you set a delay that is equal to or greater than the TTL of Exchange Autodiscover CNAME DNS records (3600 seconds by default).
Also, the following command can be used to clean up the DNS cache on a client machine running Windows:
ipconfig /flushdns
How to limit the number of simultaneously running migration tasks
Migrating Exchange subscription involves multiple tasks that are executed by Task Manager in Odin Automation. Migration tasks related to the same subscription are executed one by one; migration tasks related to different subscriptions are executed in parallel.
The overall number of simultaneously running tasks is limited in Task Manager. As a result, if a lot of Exchange subscriptions are migrated in parallel and there are a lot of running migration tasks, Task Manager may reach the limit of simultaneously running tasks so that other tasks, including tasks non-related to migration, will be postponed. To prevent this, you can limit the number of simultaneously running migration tasks (see the instruction in the internal part of the KB article).