Office 365/Shared Mailboxes/Best Practices/Caching

Hello all,

We recently migrated from in-house Exchange to Office 365.

At this firm, a lot of the assistants have Full Mailbox Access to their lawyer's mailboxes (sometimes they have access to two or three of them). We are experiencing performance issues when the assistants do things like: selecting multiple messages, deleting multiple messages, moving large emails...those kinds of things.

I am confused as to how cache mode works in this case. I would assume it would be best to have all of mailboxes an assistant has access to to be cached locally. However, when I look at the data file folder location, the only OST is for the assistant's mailbox. I would have thought to see an OST there for each shared mailbox.

How do I get it (if that is actually what I want) to get all the mailboxes they have access to to be cached locally?
Is there a problem with it auto-mapping?
Do I need to setup their profile, or their specific Exchange account, in a specific way?

Thanks for taking the time to read this question.

(PS: Please no suggestions of 'Get the lawyer to shrink their mailbox size'. It just ain't gonna happen.)
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Vasil Michev (MVP)Commented:
It will be cached in the same OST. And you will get issues once the OST size goes too large.

If you want a separate OST, configure it as additional account (i.e. add it via File -> Add account and not via Account settings -> More -> Advanced. And no, you don't need the lawyer username and password, just use the assistant's ones.)

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tnormanAuthor Commented:
The size of the assistant's OST is currently the same size as her mailbox; both are about 3 GB. The one lawyer's mailbox is in the area of 10 GB. I was wondering about the 'one OST' thing, but wouldn't her's then be about 13 GB?
Vasil Michev (MVP)Commented:
Seems the laywer one is being accessed in Online mode. Or if she's using 2013/2016, the 'cache slider' is set to download only a subset of the messages (similarly, filtering might be configured on some of the folders).
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