Prevent and Remove Microsoft Outlook Duplicates

August 22, 2008

This page contains answers to common problems about Microsoft Outlook duplicates, where they come from, and how to avoid them. All of the information contained pertains to Microsoft Outlook, not Outlook Express. To find out more, including the differences between Outlook and Outlook Express and how to find out which one you use, see our general FAQ.

This page is broken up into two parts, how to prevent the duplicates from occurring in the first place and how to clean up the duplicates.


Many things cause duplicates to appear, including synchronization with Palms, Blackberrys, or Pocket PC PDAs, restoring Exchange public folders from backups, using Netfolders, incorrect Outlook rules and many other reasons. Preventing them from occurring in the future is the first step to eradicating them.

1. How to stop receiving duplicate email messages
2. How to prevent sending duplicate email messages
3. How to prevent seeing duplicate names when viewing the “Select Names” window after clicking “To:”
4. How to prevent duplicate appointments


Removal is the second step to eradicating the duplicates. Once you are sure that no more duplicates will be created, you can use these methods to clean up the duplicates.

1. How to remove Outlook duplicates, including email, contacts, appointments, and tasks
2. How to remove duplicate Outlook Today and Personal Folders
3. How to remove duplicate Outlook address book entries
4. How to remove duplicate holidays
5. How to remove duplicates due to Netfolders

1. How to stop receiving duplicate email messages

There are a few things you can check to stop duplicate email messages.

Start by checking Rules to be sure that copies are not being made to the Inbox, and make sure that all your rules end in “Stop Processing” actions.

Then check the task manager to be sure that there is only one instace of Outlook running. Two instances of outlook.exe running can produce two messages arriving at the same time. You will need to then determine why two instances of Outlook were running in the first place.

Another thing you can do is to delete/remove ALL your e-mail accounts and recreate them. This worked for some people.

Also, if your running Outlook XP, be sure that you are at service pack 2 or later. You can tell if you need to upgrade at Microsoft Product Updates.

Finally, another person had this happen when he had two e-mail accounts set up – using two e-mail addresses, but the same POP3 incoming and same SMTP outgoing. What happened is that the second account was getting the e-mails from the POP3 server before they were actually deleted after the first account was finished. If this is the problem you can disable the receive on the second account. There is a Microsoft article explaining the problem more thoroughly at

2. How to prevent sending duplicate email messages

Sending multiple email messages can be the result of Norton Anti-Virus and Outlook combined. Apparently when Norton scans outgoing emails it may send it out twice. The quick fix is to change the Norton properties to not scan outgoing messages, but you may want to consult the Symantec Knowledge Base about your software.
3. How to prevent seeing duplicate names when viewing the “Select Names” window after clicking “To:”

What you may be seeing is an entry for an email address and one for business fax numbers. This is because Outlook considers fax numbers as “valid transport addresses”. You can prevent these duplicate names from appearing by prepending “Fax:” before the number in the contact. This has the effect of preventing Outlook from seeing the fax number as a valid transport address, so you only get one name (the email address). This technique is useful…

[Editor’s note: Shameless self promotion warning]
…if you have too many contacts to process, and you can either export them all to Excel, change the numbers, then import them back, or you can use our Hide Fax Numbers add-in to process them all. The add-in has recently been updated to automatically process the fax numbers in contacts as you add them.

In addition, there may be other solutions that exist. See the Resources page for more information about these solutions.

4. How to prevent duplicate appointments

Check to see if you have more than one Outlook running. Having more than one Outlook process running while synchronizing can lead to duplicate appointments. To see if you have more than one running, quit Outlook, open the Task Manager and go to the processes tab. Once there, click once on the “Name” column to sort alphabetically, then look for “Outlook.exe”. If it’s listed there, then highlight it and click on “End Process”. Some people report finding up to four copies of Outlook running using this method. You should be able to resume your synchronization after performing this step.

Duplicate appointments can also be created by accepting a meeting request in Outlook Web Access. See the Microsoft knowledge base article titled “A duplicate appointment item is created when a user accepts a meeting request in Outlook Web Access” for more information about this.

1. How to remove Outlook duplicates, including email, contacts, appointments, and tasks
If you have just a few duplicates, it may be easiest to manually remove them. For emails, this is no problem but for any other Outlook item it is easiest to view the items in a table view, then select the duplicates, then delete them.

To accomplish this, go to View…By Category (or “By” anything really). This gets the view into a mode you can work with. Click either names or subjects (or any shown field) in the column header (in the gray area) to gather similar items together. You can then delete all the duplicates you find.

[Editor’s note: Another shameless self promotion warning]
Sperry Software offers 8 different Outlook duplicate eliminators, including a bundle package comprising all 8 for one price. We are aware of cheaper and sometimes free solutions to resolve duplicates (see the Resources page). However, it is our hope that you will support us by purchasing our products so that we can continue to maintain useful pages like this one.

2. How to remove duplicate Outlook Today and Personal Folders

There are three things you can try:

1) Right click on the folder and select “Close”.

2) Close Outlook, then right click Outlook Icon on the desktop. Select Properties, select Data Files. Remove the links to the backup .pst file.

3) Under the folder named HKEY_CURRENT_USER\Software\Microsoft\Windows Messaging Subsystem\Profiles\Microsoft Outlook Internet Settings you will have a series of folders with long hexadecimal numbers. Two of the folder will point to your *.pst file. You will next to export one of them (Registry | Export registry) and then delete the exported hexadecimal folder. Start Outlook, if it is fubar. Close outlook and import the registry file you just exported. Export the other hexadecimal folder and delete it. Start Outlook again.

If this is too scary, you can do this.

1) Export the folder named HKEY_CURRENT_USER\Software\Microsoft\Windows Messaging Subsystem\Profiles\Microsoft Outlook Internet Settings

2) Delete the folder named HKEY_CURRENT_USER\Software\Microsoft\Windows Messaging Subsystem\Profiles\Microsoft Outlook Internet Settings

3) Go to the folder named HKEY_CURRENT_USER\Software\Microsoft\Windows Messaging Subsystem\Profiles\

4) On the right, delete the value named: (Default Profile) “Microsoft Outlook Internet Settings”

Now you can start Outlook. Outlook will start like it is in a first run condition and you will have to open your old *.pst file via a File | Open | Personal Folders. Select View | Folder List. Right click on Personal Folders (the one that doesn’t have Outlook Today next to it) and select properties. Near the bottom is a checkbox to have mail delivered to this set of folders, check it. Restart Outlook and you’re all set.

In addition, see this Microsoft Knowledge Base article “OL2000: Duplicates of Outlook Today and the Folder List Appear in Outlook”

3. How to remove duplicate Outlook address book entries

In Tools…Addressbook you may have to pick from a list that looks like this:

Outlook Address Book

Where only the last one has any contacts.

The way to remove this condition is to go to Tools…Email Accounts…Directories…View or Change. Select your Outlook Address Book service, then change. On the next page, delete the first 3 contacts folders that appear. Close and restart Outlook and they should be gone.

4. How to remove duplicate holidays

Highlight the calendar, go to View…By Category and look at the Holiday category, then manually select and delete the duplicates.

This Microsoft Knowledge Base article may also help: How to Add and Delete Holidays in the Calendar.

5. How to remove duplicates due to Netfolders

Netfolders has been known to cause bugs and the feature has been taken out of Microsoft Outlook 2002. The only suggestion received so far has been to try deleting the net folders share and recreating it.
More Information From Microsoft

How to Clean Up Duplicate References to the Same .pst File
Multiple Personal Address Book Imports Cause Duplicates
Importing a Personal Distribution List from PAB May Cause Duplicate Contacts

Sperry Software would like to thank these Outlook MVPs without whom this page would not exist. In case you don’t know, MVPs are volunteers that spend time on various newsgroups, forums and web sites donating their time and knowledge to helping people overcome their difficulties with Outlook.

There are many kinds of MVPs, and the official MVP web site has more information, and many MVPs have their FAQs stored at

  • Vince Averello
  • Jocelyn Fiorello
  • Sue Mosher
  • Diane Poremsky
  • Ken Slovak
  • Milly Staples
  • Russ Valentine



How to record multiple session iso files on a CD or DVD

August 22, 2008

CDs will be readable in Unix, Linux, Windows, and MacOS with original file names

  • CDs recorded with the following options will be readable on all OS systems (Unix, Linux, Windows. MacOS) and have correct long file names in every OS.
  • The following procedures use cdrtools (mkisofs & cdrecord).
  • The procedures below work for single and multiple recording of iso images onto a single CD or DVD.
  • This note explains the procedures on Linux, Unix, Cygwin in Windows, and MacOSX systems.

Table of Contents

  • Information Common to the different systems
  • Linux, Unix, Windows/Cygwin Instructions
  • Apple MacOSX Instructions

Information common to the different systems

  • Directories to be backed-up should be placed in a common top directory.
    This directory’s name will not appear on the recorded CD.
  • CDs can contain a maximum of 600-700 Megabytes
    DVDs can contain 4.5 GigaBytes of information
  • mkisofs options for the recording
    • The recording will be readable on Linux., Unix, Windows, Apple systems with original long file names
      if the following options are used: -rJTV vol_name
      eg: /usr/bin/mkisofs -rJTV data0303 ./data > data.iso

      • r – is for rockridge extensions – long file names
      • T – sets up Translation Table – r & T for Unix/Linux systems
      • J – Joliet extensions – for Windows systems
      • V – creates a volume title which will appear on Windows/Mac/Solaris systems
        Keep the same title when recording multiple sessions – otherwise only the last title recorded will be used (on some operating systems).
      • Other useful options
        -a: Include all files – “~” “#” files
        -l: if very many files are in the directory, you might need this one – but it may cause problems on Windows
        Read the man page
    • You need a machine with a CD writer to find the information for the next mkisofs session (for a multi-session CD).
    • Use CD-R recording material instead of CD-RW. A CD-RW will be readable only on machines with a CD writer. This excludes all the CIMS Suns and SGIs.
    • On a CD-R, a multi-session recording will obscure older versions of the same file and add new files and directories to the disk.

Linux, Unix, Windows/Cygwin Instructions

  • In the following commands, I use “Data0303” for the volume name, and “data” for the top directory containing the directories to be recorded.
  • mkisofs can be used on any system having this command (Suns, SGIs)
    cdrecord has to be used on a system with a CD writer.
  • cdrecord -scanbus
    This only has to be done once on a system to obtain the device numbers
    On the Dell linux system in the AML lab the results of this command is:
    0,1,0 1) ‘SAMSUNG ‘ ‘CDRW/DVD SM-308B’ ‘xp01’ Removable CD-ROM
    This means: dev=0,1,0 or dev=ATA:0,1,0 will be used in subsequent commands.
    Some systems need the device to be specified with ATA: before the device numbers. (The reference to the CD/DVD player can be seen in the boot messages.)
  • create a top directory and move directories to be recorded into this directory on the machine where mkisofs is being used:
    mkdir data
    mv dataA dataB data
  • run mkisofs the first time
    /usr/bin/mkisofs -rJTV Data0303 ./data > data1.iso
  • Move directories dataA dataB back to their original places
  • cdrecord -v -eject dev=0,1,0 -multi speed=8 data1.iso
    (or if necessary: cdrecord -v -eject dev=ATA:0,1,0 -multi speed=8 data1.iso)
    speed is the speed of the CD recorder – in the ViSLab it’s 8x
  • All subsequent times mkisofs has to know where the free space begins.
    This is obtained with the CD inserted in the CD writer and the cdrecord command
    cdrecord -msinfo dev=0,1,0
    or cdrecord -msinfo dev=ATA:0,1,0
    The results of this command is then used with the -C option in mkisofs

    • If mkisofs is on different machine than the CD writer and cdrecord
      copy the info from: cdrecord -msinfo dev=0,1,0 and put it after the -C option in mkisofs
      /usr/bin/mkisofs -rJTV Data0303 -C {cdrecord info} -M /dev/cdrom ./data >data2.iso
    • If the mkisofs command is on the same machine as the cdrecord
      • either
        bash shell: NEXT_SESSION =`cdrecord -msinfo dev=0,1,0`
        tcsh or csh shell: set NEXT_SESSION =`cdrecord -msinfo dev=0,1,0`
        /usr/bin/mkisofs -rJTV Data0303 -C $NEXT_SESSION -M /dev/cdrom ./data >data2.iso
      • or combine these 2 commands
        /usr/bin/mkisofs -rJTV Data0303 -C `cdrecord -msinfo dev=0,1,0` -M /dev/cdrom ./data >data2.iso
  • Then record the iso file
    cdrecord -v -eject dev=0,1,0 -multi speed=8 data2.iso
  • When finished recording, eject the disk: eject or press the button on CD drive.
  • Re-insert the CDROM and check it
    • On a Linux system
      ls -F /mnt/cdrom
      dataA/ dataB/ dataC/ dataD/ …. TRANS.TBL
    • On a Sun: the disk is in /cdrom
    • on an SGI: the disk is in /CDROM
    • For further information on this and other types of CD burning,
      see the Linux:CD writing HowTo

Apple MacOSX instructions

  • Pre-Instructions and Comments
    • the MacOSX instructions are slightly different from those for the other OSs
    • the procedure has one peculiarity in that you have to use the command
      disktool -u disk1 0
      from time to time to disassociate the device with MacOSX without ejecting it.
      Below you’ll find this command listed each time I needed it during the test writing session on the G4 in the AML ViSLab.
      If you have any trouble issuing a command, use disktool first.
    • The G4 in the AML ViSLab is a SuperDrive and thus the device is called “IODVDServices” in the following instructions.
    • In the following, I will call the common top directory with the data to be recorded: data
      and the name of the CD: Data0303
  • Put your data directories to be recorded in the common top directory data
  • Create the first iso image
    mkisofs -rJTV Data0303 ./data >data1.iso
  • burn this first image
    cdrecord -v -multi -data dev=IODVDServices data1.iso
  • disktool -u disk1 0
  • Find the information locating the free space on the CD
    set NEXT_SESSION=`cdrecord -msinfo dev=IODVDServices`
  • disktool -u disk1 0
  • create next ( and subsequent) iso image
    mkisofs -rJTV Data0303 -M IODVDServices -C $NEXT_SESSION ./data >data2.iso
  • disktool -u disk1 0
  • burn the next( and subsequent) iso image
    cdrecord -v -multi -data dev=IODVDServices data2.iso
  • when finished eject the disk
    hdiutil eject disk1 or press the “triangle” button key at the top right.
  • Re-Insert the disk and type:
    ls /Volumes to see the results
  • For further information see Create single-volume multi session CD-Rs