Exchange Online vs Caching

Good day,

I have a few users mailboxes that are much larger than the "safe" size.

As i understand an OST should not be larger than 25GB. I have some users that are close to 50 and 1 or 2 that is over 50. I had to edit the registry to allow the ost to grow larger than 50.

I believe the answer is to let these users use their mailboxes online and Outlook not to cache emails. I don't have experience with this and I want to know what the challenges are if i do disable the caching of emails -  specifically search ability of old emails and connectivity external from the office.

Thanks in advance.
Leroy LuffHead of IT & DIgitalAsked:
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If you disable caching. Reduce the mailbox size by downloading emails to local PST.

You will experiencing issues working outlook in offline mode.
Difficulties in connecting such a huge mailbox using outlook. It will be slow.
Another option would be using an automated cloud solution.  Example: Symantec Enterprise Vault.
Thomas Zucker-ScharffSolution GuideCommented:
Users should be aware that large mailboxes, either with an ost or archiving using pst, will cause a slowdown in their computers.
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Will SzymkowskiSenior Solution ArchitectCommented:
When you use Outlook in Online mode you are using the Exchange Server Resources and Network resources to capture the data that is presented in your Outlook client. If you have users with very large mailboxes then cached mode and online mode will not be good for either.

cached mode
- cached mode OST can become corrupt very easily after reaching 10+ GB
- extra storage on local machine for OST

online mode
- using network and Exchange server resources

Possible solutions
- use Outlook 2013, it has a new feature for cache mode which will let you cache a percentage of mail (6 months) and then the rest is located on the server.

This could be a good option if Archiving is not. This will allow the user to keep recent mail cached and older email on the server. Outlook will use local resources when searching for emails in the OST and only use Exchange resources when the OST does not contain the emails.


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Leroy LuffHead of IT & DIgitalAuthor Commented:
Thank you for the insight WIll - much appreciated.
Thomas Zucker-ScharffSolution GuideCommented:
It depends what you mean by archiving and what the user will do.  My users tend to archive and then open the archive pst in their outlook.  This practice makes their machines slow down, because they are still loading the large amount of data they were before.  When users archive they should NOT open the pst file unless absolutely necessary, and then close it when they are done.
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