If you’ve been working with Microsoft Outlook for long, and particularly if you’re working in a Exchange Server environment (which set some pretty strict limits on file size), your Outlook .pst file may be getting too large. While you may not want to adhere to the fabled Inbox Zero standard, doing a little mail maintenance periodically will help Outlook run better. Here are five strategies for paring down your .pst file’s size.

Unless otherwise noted below, all instructions and screenshots are for Microsoft Office 2010 for Windows.

Groom your Deleted Items folder

You’re really good about deleting Inbox messages you no longer need, right? But if they’re not being removed from your Deleted Items folder, they still count toward the total Outlook file size.

You can empty the Deleted Items folder one of two ways: manually or automatically. To do this manually, right-click on your Deleted Items folder, choose Empty Folder, and they’re gone.

If you’re confident enough to say that, when you delete an e-mail, you never want to see it again, choose the automatic option. Go to the File tab and choose Options, then click Advanced. Under Outlook Start and Exit, you’ll see a checkbox next to “Empty Deleted Items folders when exiting Outlook.” Check that and click OK to save the setting.

Eliminate duplicate e-mails

Every time you forward an e-mail (particularly with attachments) to staff members, you are effectively doubling the size of storage necessary for that information, since by default a copy of that e-mail with its attachments now resides not only in your Inbox but in your Sent Items folder as well.

If there’s no longer a compelling reason to keep the forwarded version of that e-mail, go ahead and delete it out of your Sent Items folder. One trick to make this easier is to sort the e-mails in your Sent Items folder by recipient. It’s easy – just click on the To header in your Sent Items folder:

(You can simply instruct Outlook not to save forwarded messages in your Sent Items folder via a setting in the Mail/Save Messages section under Outlook Options accessible via the File tab. By default, however, any message you send, forwarded or not, is saved in the Sent Items folder.)

Save individual e-mails

Many Outlook users don’t realize they can save individual Outlook e-mails outside the Inbox in a variety of formats. Simply open the e-mail, go to the File tab, and click Save As.

You can save the e-mail as a plain text document, or you can save it in the Outlook Message format (.msg), which will preserve the formatting of the original e-mail.

Since any attachments to that message are saved in a temporary folder in Windows, it’s probably a good idea to right-click on any attachments and save them separately in the same folder on your hard drive (and make sure it’s backed up frequently).

Archive to Adobe Acrobat

If you’re ready to close a particular matter, and you got all the relevant e-mails sorted into a subfolder under your Inbox, you can use Adobe Acrobat to create an archive file that you can save your electronic records. The latest version of Adobe Acrobat include some pretty cool tools for archiving e-mail. In any version, the result is a conveniently searchable archive in a format virtually any computer can use.

Archive via Outlook

Once you’ve been using Outlook for multiple years, you may want to get into the habit of archiving your Inbox and Sent Items folders annually (or even more often if necessary).

It’s possible to automate this archiving, but since that tends to slow down the computer if you’re dealing with a large volume of e-mail, you may want to set this up manually and go to lunch. To start archiving a particular folder, go to the File tab, and under Cleanup Tools, choose Archive.

Choose the folder you want to archive (and be aware that all subfolders under that folder will be archived as well), choose the “older than” date, hit the Browse button if you want to specify a particular location and/or file name, then click OK. Depending on the volume of e-mail you’re processing, this is going to take a little while, so take a break from the computer.

Once the archive is complete, you have a separate .pst file with the older e-mails intact. If you ever need to access them again, simply go to the File tab, click Open, then choose Open Outlook Data File.

The “stitch in time” approach

If you can work some of these strategies into your regular routine, you’ll be far ahead of colleagues who suddenly can’t send or receive e-mail because their Outlook file has gotten too large. A little maintenance here and there will save you from a similar fate.

(photo: http://www.flickr.com/photos/redjar/113152393/)

  • File this under “I can’t believe I forgot to mention this” [under “Eliminate Duplicate Emails”] …

    There is actually a way to NOT save an individual email to your Sent Items. Before you click “Send,” go to the Options tab, and on the right there’s a button called “Save Sent Item.” Click that and choose “Do Not Save.”

    • This makes me a little nervous. If I understand you right, I’d lose the contents of the sent email if no reply comes back.

      • By default, all your outgoing email is saved in the Sent Items folder. If you’re sending something you don’t necessarily need to save for future reference (like simply forwarding an email with an attachment to your assistant with the instruction “print this”) then you can simply set the forwarded email to NOT be saved to the Sent Items folder, thus saving some space (particularly if the attachment is large).

        That’s really the only situation in which I’d really consider NOT saving something to Sent Items.

  • Thanks for the additional tips. I’ve been using the archive to Acrobat regularly since starting practice and can recommend this technique highly.

  • These are great tips. Can you or Christopher give more specifics on using Acrobat to move old files off Outlook? Can you move them back to Outlook later?

  • @Steven,

    To answer your last question first, in a word, no. If you’ve converted them to Adobe and deleted the original emails, then there’s no converting them back to Outlook. Here’s a video from Rick Borstein’s Acrobat for Legal Professionals blog about converting emails to pdfs: http://tv.adobe.com/watch/acrobat-x-tips-tricks/how-to-convert-outlook-email-to-pdf/

    (And sorry for the late response — I thought I’d responded to this earlier. Must have *dreamed* I responded.)

  • Great post.

    There is also an option to NOT save a copy of Forwarded messages that is built into Outlook.

    Go to Options in Outlook and click Mail. Scroll down to the Save Messages section and untick Save Forwarded Messages.

    I have not used this myself.

    In fact my experience (when updating QuickFile for Outlook-Lawyers Edition) was that lawyers wanted a copy of all emails they send in their sent items (even when they file a copy elsewehere)…. this feature was eventually implemented as a result of their requests/demands.

    The feedback was that it makes it easier to find emails later and also to fill in timesheets etc at the end of the day.


    • Yeah, I know a lot of lawyers who use their Outlook Inbox/Sent Items to help them fill in their timesheets!

      • I never delete anything from sent folder or inbox. I need to keep a record, even if it’s as inane as “print this.” I archive by folder and year. If you have a bunch of emails startgin in 2010 you can archive your sent box this way:

        Archive all files older than 1/1/2011 to archive-sent-2010. Then run it again for 2011 and 2012. Do the same for the inbox.

  • Ankit

    I have a question, I had a pst which I copied it in another folder.
    I accidentally mapped another pst and I do not have the same emails.
    How do i shrink it to one?
    I cannot manually move the mails, they are in huge number….
    Need help!


    • @Ankit – Have you tried File | Open | Import? Without knowing what version of Outlook you’re using, I can’t get any more specific than that.

  • Ankit

    Thanks a lot, that served the purpose, I am using Outlook 2010, the enterprise version, thanks again…..



  • RobertOscar

    nice blog. I used SysTools split PST tool to shrink my PST size and i found 100% satisfactory result.

  • dannwebb

    Why does the link “pretty cool tools for archiving e-mail” go to a page about “observations about rural steriotypes” ??

    • I have no idea, but it doesn’t any more.

  • Zeke Teke

    Hello! Can anyone tell me if my user has a large PST file store locally and opens with Outlook can cause performance issues?

    • Yes, big PST files can cause performance issues. Hence this post on shrinking them.

      • Zeke Teke

        sorry, I was envisioning differently as I was reading this article with server storage in mind as opposed to a local PST. But just to clarify then, it is better to have a few smaller PST files in outlook than one larger one, yes?

        • Smaller is better, yes. Outlook seems to have trouble with larger files, although I’m not exactly sure what the recommended limit is, these days.

  • Russell Smith

    In my opinion, archive process is best tactic to shrink PST file into smaller parts. In current scenario, MS of Outlook users are trying advanced mode of archive process which is splitter mechanism. There are several products available in market for shrinking PST size effectively. Stellar phoenix pst file splitter is one of them.

    • Martin Hoff

      Hello Russell,
      I have taken a trial of Stellar Phoenix PST File Splitter. Now, I am planning to suggest this software to IT department of my organization.

  • Randall Shorr

    I auto-archive my main PST file, but now the ArchivePST file is too large (such that I’m getting an error message suggesting I permanent delete items from the archive). Can I instead start a NEW archive file, and thereby maintain all of the items in the current archive file? Alternatively, can I split the ArchivePST file and move the older items into a separate archive file?