Huge .pst file in IMAP

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Outlook version
Outlook 2010 64 bit
Email Account
Hi, can anyone explain me why my .pst file of the account, which is set up in IMAP, has 13GB size? I thought that in IMAP all the emails are stored on the server and they are not downloaded to .pst file like in POP. I've noticed that when I set up IMAP account it creates 2 .pst files and one of them cannot be used as a default account. What is that file for, why it cannot work on it's own and what is stored inside it?
IMAP mail is stored on the server but are synced to a pst file so they are available if you are offline. Your calendar and contacts are stored in the default pst file and your imap mail is in the other pst file.

Do you have that much mail online? It seems large - unless its a gmail account, then it sounds like you are syncing the All mail acccount, which will double the pst size as its a copy of all mail in the mailbox.

See the section near the bottom of the article about subscribing to folders for instructions and screenshots - - you can unsubscribe from any folders but the default folders in any imap account, but definitely unsubscribe from all mail if you are using gmail.
Hello Diane,
Many thanks for your quick reply.

It's a gmail account and there are emails from up to 5 years ago. All mail folder is there. I'm going to unsubscribe it.
So just to make sure; IMAP .pst file (if that what it's called) stores ONLY synchronised emails from the server? If I delete that .pst file no data will be lost (contacts, notes, taks etc.), only that email account will be deleted which was using that .pst file?
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