How to Merge Important Emails without Duplicates in multiple Outlook PST Files

  • Written By Eric Simson

  • Updated on August 19, 2020

  • Min Reading 5 Min

Outlook PST becoming too clustered? Herein is a solution for you. In this piece, we’ll be showing you how to merge important emails and remove duplicates in Microsoft Outlook PST files.

Outlook’s mailbox could easily become clustered, placing undue pressure on the host PST. Typically, emails that are supposed to be together are saved as individual email messages, and in some cases, some of these emails are even duplicates. With this scenario, the host PST is continuously stretched, until it eventually becomes oversized, leading to severe file damage or corruption.

To prevent this, we’ll be showing you how to use a standard Outlook solution to sort out your PST files, by merging important email messages without duplicates. Read on!

How to Merge Important Emails without Duplicates in Outlook PST Files

Firstly, it is important to note that merging of emails and removing duplicates are not repair procedures, but rather file management procedures. Hence, these two procedures are practically beyond the scope of the Inbox Repair Tool (ScanPST.exe). Nevertheless, both procedures serve as preemptive measures, which would go a long way in preventing your PST from becoming oversized and eventually corrupted.

As it stands, getting a reliable stand-alone Outlook email merger or duplicate remover is a futile exercise. However, there are tools that offer both packages in one single solution. And one of the best available tools in this regard is Stellar Toolkit for Outlook, which is an all-in-one Outlook/PST repair and file management package.

Stellar Toolkit for Outlook: Duplicate Remover & PST Merger

Quick Solution:  Stellar Toolkit for Outlook is a comprehensive solution, which offers you just about everything you need to achieve optimum, hitch-free, experience in Microsoft Outlook. Two of the most important modules here are the “PST merge” and the “duplicate remover”

For further clarity, we’ll be looking at these two modules individually.

PST Files Merger

Outlook saves emails, calendars, attachments, notes and contacts among others as individual PST files, irrespective of the files’ subject. Put aptly, Outlook can save important PST files as individual files, even if they are from the same sender or for the same recipient. However, while you are afforded the opportunity of merging similar (or important) PST files manually, the process is quite cumbersome. Typically, the “manual merging” process ends up increasing the mailbox size. And this consequently puts a strain on the host PST, resulting in the very thing it is meant to prevent – oversized PST.

Therefore, to safely merge emails (and other PST files), Stellar Toolkit for Outlook’s PST merge module is your best bet. With this module, you can easily merge multiple PST files (in different formats) and save them as a single file (in a single format), without the risk of losing your emails.

Interestingly, this is achieved in only a handful of clicks, as described below:

  • Get Stellar Toolkit for Outlook.
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  • Upon successful installation, launch the toolkit.
  • In the home window, showing all the eight modules, locate the “Merge Outlook PSTs” module and click on it.
  • In the next window, showing the “Stellar Merge Mailbox for Outlook” interface, select and add (drag and drop) the emails (or files) you want to merge.
  • Click on the “Merge” icon and select the PST to join.
  • From the root node, select the folders which you want to merge. Make a check to automatically select complete mailbox / all the folders. In Home menu, select desired options from Exclude Items, Default Duplicate Criteria and/or Advanced Duplicate Criteria to remove duplicate mailbox items.

Note: Advanced Duplicate Criteria is enabled only when you select Default Duplicate Criteria.

  • Click on “Join” and wait for the process to run.
  • Voila! Your emails and other selected files would become merged into a single PST file.

With the above procedure, involving Stellar Toolkit for Outlook, merged files are kept in their original states, and each of them can easily be recovered, if need be. Also, should you have a password-protected email you wish to merge, the tool would easily go around it.

Lastly, during the merging process, the tool identifies and removes inherent duplicates, to ensure only necessary files are merged.

Duplicate Remover

As pointed out earlier, Stellar Toolkit for Outlook filters out duplicate files during PST merging process. However, this is not applicable to files that are not selected for merging. Hence, to resolve this, Stellar Toolkit for Outlook provides a designated duplicate remover to effect the needed changes.

Typically, an Outlook mailbox is often saturated with tons of duplicate emails, and in some cases, these include attachments (of various sizes), calendars, journals, notes and contacts among others. This constitutes one of the most notorious causes of storage issues in Outlook, which eventually results in “oversized PST”.

To address the issue, you can easily deploy the “duplicate remover” (in Stellar Toolkit for Outlook) to remove duplicates and restore normalcy to your Outlook program.

Below is an outline, showing the necessary steps to remove duplicates in PST (using Stellar Toolkit for Outlook):

  • After installing and launching the toolkit, go to the home window, click on the Remove Duplicate Email icon.
  • In the next window, click on the Stellar DeDuplicator for Outlook add-in folder.
  • Select the prompted folder and other desired options.
  • Follow the prompt commands to move duplicate files to a different location or simply delete them.

By using Microsoft Outlook Toolkit to remove duplicate emails (and other PST files), you’re able to remove, not only duplicate files, but also the nonessential ones that are choking up your storage space. The duplicate module is available for all versions of Outlook between v2019 and v2003.

Essentially, with the “duplicate remover” module, you’re able to recover significant storage space in your Outlook PST profile. With this. you can worry less about your PST becoming oversized.

It is pertinent to point out that Stellar Toolkit for Outlook, which incorporates the “PST merger” and “duplicate remover” modules, does not come cheap. As a suite of tools that incorporates a total of eight standard Outlook repair and file management tools, it offers a fair deal.

However, you can install and test-run it for free, for a limited period of time, before committing your funds to make the purchase.


This tutorial has stressed the need to merge important emails and remove duplicates in Microsoft Outlook PST files. And we’ve recommended Stellar Toolkit for Outlook, specifically the “PST Merge” and “Duplicate Remover” modules, to facilitate the processes.

Furthermore, for users’ convenience, this tutorial has outlined a summary of guidelines, showing how to apply the requisite modules (PST merge and duplicate remover).

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