Mac Outlook 2011

Hi  guys,

i just want to check if how can i make a offline mails in outlook 2011.

i try to move to my inbox to " on my computer"

my account is imap.gmail.com.

when i am trying to drag or move to offline (on my computer).

the capacity is still the same.

i have 30 gb storage capacity.

now i have 32.49 gb on my account which i cannot receive any mails because its full already.

now i want to make the emaills to be offline.

in mac outlook under "ON MY COMPUTER". i create folder of INBOX 2013, INBOX 2014 AND INBOX 2015 (for january to july).

and SENT ITEM 2013, SENT ITEMS 2014 AND SENT ITEMS 2015.

now when i am moving the inbox mail from january to december 2013. (i try to drag / move) but what happen is the storage capacity still 32.49gb.it is not decreasing.

my account is imap.

what should i do to make my mails to be OFFLINE?

your help/ reply is appreciated.

ROD