Removing redundant messages
If you and one other person have been involved in an email conversation which consists entirely of responses to each other following the original email, it is pointless retaining any of the messages except the final one. Use the Clean-up Folder option to retain only the last email of a conversation between you and the other person. (Note: clean-up is applicable only for emails between 2 people.)
To use the Clean Up Folder tool and remove all messages in a conversation except for the last one:
Select the folder or conversation you want to clean up.
On the Home tab, select from the list of options available for Clean Up.
If no messages suitable for clean-up are found, you will get a message telling you so. Otherwise, relevant messages will be moved to your Deleted Items folder or an alternative folder you’ve designated (see point 3 below). This is a safety feature. After performing a Clean Up, you can check the folder to ensure that only redundant messages have been moved there. Simply drag any message you want to keep back to the appropriate folder. Then delete the rest.
Note: The Clean Up Folder option appears when you right-click on a folder, but it will be greyed out unless caching is turned on (see Check and/or change cache settings for Outlook below). However, turning on caching can create other problems so it is generally best to avoid it and use the method described here instead.
The 'clean up' option is unavailable when I right-click on an Outlook folder
I’ve turned on Show as Conversations on the View tab so that related messages are grouped together. Now I want to use the ‘clean up’ option to get rid of redundant messages, but it’s greyed out. How do I fix this?
The ‘clean up’ option is available via right-clicking only if caching is turned on. (See the Note at the end of point 'Removing redundant messages' above.)
Moving 'cleaned up messages' to a designated folder
If you want to keep ‘cleaned up’ messages separate from your Deleted Items until you can check them, you can create or designate an existing folder for this purpose. Go to the File tab > Options > Mail and scroll down to the Conversation Clean Up section.
In the example above, the 'cleaned up items' will go to a folder named 'Cleanup. If this box is empty with no folder selected, cleaned up items will go to the Deleted items folder.
To change the location cleaned up items go to, click on Browse and choose or create a new folder (such as Cleanup). When you click OK, the new location will be shown as in the example above.
Check and/or change cache settings for Outlook
To check and/or change the cache setting:
Go to the File tab > Info > Account Settings > Account Settings button. The Account Settings dialog box opens.
Click once to select your account and click Change. The Change Account dialog box opens.
Check to see whether Use Cached Exchange Mode is ticked, and change it if desired.
Click Next until Finish is available.
Note: with caching turned on, Outlook will not be updated as frequently as it is otherwise. If you go ahead anyway and this becomes a problem, repeat the steps above to turn caching off again.