Our query is basically to understand how Outlook 2013 works. So lets assume a scenario as below.

• We connect to Exchange Online Mailbox with the Outlook 2013 Slider set to cache One years mails.
• At the end of first year of using outlook 2013, the OST file size has grown to 3.5GB

Our Queries

1. Assuming the mail transaction in the second year, by size and number, is just half the amount as compared to first year, will my .ost file size shrink automatically below 3.5GB at the end of 2nd year?
2. If the answer to the above query is YES, then is there any Microsoft document stating so?

• Edited by CosmicStorm Monday, June 15, 2015 11:14 AM

No, it will not shrink automatically but you need to use ost crop tool to cut the size of ost file.

Dear Kenny,

Your reply contradicts what answer i received here http://answers.microsoft.com/en-us/office/forum/office_2013_release-outlook/outlook-2013-ost-size/6b019ef3-26c9-4061-8889-dd236bb190b8

Hi,

This document should be helpful for you:

Plan a Cached Exchange Mode deployment in Outlook 2013

https://technet.microsoft.com/en-us/library/cc179067%28v=office.15%29.aspx?f=255&MSPPError=-2147217396

Best Regards.