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New Friend (or an Old Friend who Built a New Account)
Posts: 81
Reply with quote  #1 
The starting point is an environment that is almost 100% virtual (besides the ESXi hosts, obviously). Outlook uses online mode as opposed to Exchange cached mode. To be clear, this is Exchange on-premises, not to be confused with "Exchange Online" (Office 365). 

Now let's suppose that the organization moves to Office 365 with Exchange Online (Online with a capital "O").

Client machines will remain virtual and hosted on-premises.

Desktops are persistent. I'm not sure if that will change in the future.

Is it recommended to use Exchange cached mode with Office 365?

On one hand, Outlook working directly with the mailbox in the cloud would seem to require a very low-latency connection to avoid delays.

Side note: it has been made clear that slower Outlook performance would not be acceptable. User experience would have to be "equal or better" than it is now. Current on-premises Exchange / Outlook performance and stability is very good, often described as "rock solid".

On the other hand, I've heard at least one source claim that the time to update the Outlook cache every morning can take a lot of time (as in get up and get some coffee). This was in another environment. I'm not sure how accurate that assertion is and have no idea what kind of Internet connection was involved.

The organization would prefer not to have .ost files several dozen GBs large on the virtual clients.

As you may know, Office 365 mailbox maximum size is now 50 GB.

How are the rest of you managing this?


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Senior Member
Posts: 181
Reply with quote  #2 
You really need to have OST files for two major reasons.
1. You can't search a mailbox without it
2. You really need the performance

Common practice is that you redirect the OST files to a cheap storage, and have a rigorous archiving policy on the mailboxes so they would be as small as possible. Last one depending on how they use their mail

Have SpaceSuit, Will Travel

Mark Kerry

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Still Checking the Forum Out
Posts: 3
Reply with quote  #3 
I found KTools software from Google, then go to KTools Support to talked regarding migrate Exchange offline .ost file to Office 365. They provided a tool for migrating Exchange offline .ost file to Office 365. I have had completely imported .ost data to Office 365 account.

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Associate Troublemaker Apprentice
Posts: 937
Reply with quote  #4 
Exchange online mode against O365 is poor, especially with a lot of connections.

As Ton said, use cheap disk and cache, at least for the Outlook ost's.

Have you tried turning it off and walking away? The next person can fix it!

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Still Checking the Forum Out
Posts: 1
Reply with quote  #5 
This conversion is possible with  OST to PST Exporter tool. This software will help you to migrate mailboxes database from OST to PST file format. You can download free tool from here.

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