What is the Outlook.ost file for, and can I delete it?

[stanj6769]

I'm looking for files I can delete on my C drive so I can free up some space.
I found two files in my Outlook folder that I'm wondering about, since
they're pretty large (327 Mb and 341 Mb); Outlook0.ost and Outlook.ost.

What are these files; what are they for? What is the difference between
these two files, and do I need them both, or can I delete one or both of
them? What will be the result of deleting them.

Also, what is the meaning of filenames that Windows displays automatically
in blue text, vs regular black text?

 

[Vince Averello [MVP-Outlook]]

Blue text files usually mean that they're NTFS compressed files.

OST files are Offline Folder files that should be storing your Exchange
Server mailbox for offline use. I probably wouldn't delete them

 

[Roady [MVP]]

The ost-file is a local copy of your Exchange mailbox. Whether you need both
depends on your on your Exchange and mail profiles configuration.

The blue files indicate (NTFS) compressed files. While compressing files
increases space accessing these files will be (slightly) slower than
accessing it when they are not compressed.

--
Robert Sparnaaij [MVP-Outlook]
www.howto-outlook.com

Tips of the month:
-FREE tool; QuickMail. Create new Outlook items anywhere from within Windows
-Properly back-up and restore your Outlook data

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I'm looking for files I can delete on my C drive so I can free up some
space.
I found two files in my Outlook folder that I'm wondering about, since
they're pretty large (327 Mb and 341 Mb); Outlook0.ost and Outlook.ost.

What are these files; what are they for? What is the difference between
these two files, and do I need them both, or can I delete one or both of
them? What will be the result of deleting them.

Also, what is the meaning of filenames that Windows displays automatically
in blue text, vs regular black text?