Exchange Online Retention Policy Tiering

  • 9 November 2021
  • 2 replies

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How can different retentions be implemented for Exchange Online Backups?

For example 30 days on primary copy, and 180 days on secondary copy.

One can create a Storage Policy / Plan with such retentions, but as Exchange Online uses dedicated Exchange Policies for retention, this won’t achieve the desired outcome.

A mailbox can only be assigned one Exchange Retention Policy, defining how long the messages are retained for after receiving them / them being deleted, but that will take effect on all assigned backup copies.

Due to size and cost limitations, having one retention for both copies is not an option unfortunately, so I’m wondering if this is possible at all.

One idea could be to run periodic full backups (archive but select “convert to full”) and then have the secondary copy on selective, only using the monthly fulls for example. But this will create massive overhead if we have to run a full backup of all Exchange Online mailboxes once a month or so. Plus, I don’t think with that would work though, as selective backup copies can only select full backups, and even a converted archive job to full would still show up as incremental, according to this post: Microsoft 365 Exchange Online - why only forever incremental backup? | Community (


Best answer by Chris Hollis 10 November 2021, 02:22

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Hi @ChrisK

Hope you’re well.

I shared some feedback for a similar request in this thread: 

You can use a selective copy, you just have to select the jobs that you want copied / manage them on storage ‘manually’ (note the caveats I mentioned and why this can be danagerous / my preference for a Synchronous copy until the CMR is released). 

@Mike Struening also shared some handy feedback too. 

Additionally, to officially answer your question about tiered retention.. ‘primary 30 days’, ‘secondary 180 days’ etc, this will not work as you envision.. the mailbox data retention (as you mentioned / know), is based on the individual item receive, delete or retention tag settings… not job based retention like other agents / previous editions of the mailbox agent. 

Please refer to:

So if for example, you had 1/50 users with a retention policy set that defines messages are held for 8 years based on ‘receive time’, and all other users had a retention policy set for 1 year.. you then did one ‘convert to full’ job for all users, the one job you’ve run as your ‘Full’ will likely remain on the primary for 8 years (assuming a message meets the requirement of course) because not all messages within the job have met retention. 


“Due to size and cost limitations, having one retention for both copies is not an option unfortunately, so I’m wondering if this is possible at all.”

I’d personally prefer you not delete any jobs and hold out until the CMR we have raised is available, however if you are finding the footprint from the incremental jobs on your primary storage device being too excessive, the only current solution I can think of for you would be to setup a storage policy for the mailbox agent only, set primary with your required retention settings (30 days), setup a Synchronous secondary with basic days 180… then every month, check over the archive jobs on primary, ensure they have copied to secondary and then if so, delete the jobs that are 31 days+ old from the primary. 

Prior to deleting, I’d also suggest you run data verification jobs on the storage policy secondary copy to ensure the data is actually readable -

Hopefully this helps.










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@Chris Hollis thank you for the feedback and explanation. We’ll try to hold on until the CMR and will only use the manual delete option if absolutely necessary.