Hi @Prabhjot Singh
Welcome to our forum!
Please kindly note that Microsoft Q&A forum recommends asking one question per thread so we can better focus on one question.
how can we implement bandwidth constraints for 12,000 devices when new .ost files are created and begin downloading emails?
As far as I know, there is no limit requirement regarding network bandwidth in Outlook. For optimal performance, consider using bandwidth wisely from the following perspectives:
- Enable cached Exchange mode in Outlook, which allows users to use a local copy of their mailbox. This reduces the need to continuously download data from the server.
- Implement a staggered rollout of new .ost file creation and downloads. This means scheduling downloads at different times for different groups of users to avoid network congestion.
- Close apps and add-ins that you don't use often. For example, delete the peek or close the to-do bar.
In addition, we recommend that you refer to this article: https://learn.microsoft.com/en-us/deployoffice/fieldnotes/performance-recommendations.
For the second question, I noticed that you have already raised it in another thread, please focus on this thread: Migrating Devices Across Domains: Handling Old and New .ost Files.
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