.OST file , outlook, exchange

I tried to compact my mail box- OST file , i did it by going to mail icon under control panel ,

it reduced by 2Gb with outlook closed but when i opened outlook it went back to same size as original

we have outlook 2016 with mailbox on 365

how is that possible, did i miss any step, cant understand how it went back to same size after opening outlook
pramod1Asked:
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David Johnson, CD, MVPOwnerCommented:
the .ost is just a local cached copy of part of your exchange mailbox.
So either reduce the size of the online mailbox or turn off cached mode, or in account settings email account reduce the # of days you want cached.

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pramod1Author Commented:
I wanted to know how size became same after opening outlook
pramod1Author Commented:
Does it have the feature reduce no if days in outlets ok 2010
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David Johnson, CD, MVPOwnerCommented:
I don't have outlook 2010 to test but it is simple for you to check.
SysToolsData Expert - Recovery,Backup,MigrationCommented:
120915_2259_Outlook20131.png
Yes, While Selecting Cache Exchange Mode, you can also select the Time period to store the data as a backup in OST File format.
pramod1Author Commented:
Do we have this feature in outlook 2010
David Johnson, CD, MVPOwnerCommented:
outlook 2010 only has cached or not cached.
pramod1Author Commented:
so outlook  2010 has no feature of cache slider
David Johnson, CD, MVPOwnerCommented:
correct cache is all or nothing.
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