A user asked how to remove files from the Insert > Attach File menu in Outlook email.
The Attach File list comes from a mix of sources: the Recent folder in Windows, plus the Recent files in Word, Excel and PowerPoint.
To remove Office files from the list, you need to remove the files from the File > Open page in each Office app. Right-click on the file (anywhere on the file's entry row) or choose Remove from list to remove a specific file or Clear unpinned items to clear all the files on the screen. (If you have a lot of files, you may need to use Clear unpinned items several times to remove all.)
Tip: Remove from list is an option on the File > Home and on the File > Open list. Clear unpinned items is only on the File > Open List.
If files remain on Outlook's Attach File list but are not in the Office apps, open File Explorer, go to C:\Users\%username%\AppData\Roaming\Microsoft\Office\Recent and delete the shortcuts you want removed from the Attach File list.
Non-Office file types, including PDF and images, are pulled from the Quick Access list in Windows. If you want to remove these files from Outlook’s Attach File list you need to delete the items from the Recent folder at C:\Users\%username%\AppData\Roaming\Microsoft\Windows\Recent.
You can control how many recent files are listed in the Attach File menu by adding the MaxAttachmentMenuItems registry value. If you don’t want any files on the Attach File list, set the value to 0. The maximum value is 20 items, but more than 14 items is likely to require scrolling to see all.
If the Mail key does not exist, you need to create it.
HKEY_CURRENT_USER\Software\Microsoft\Office\16.0\Outlook\Options\Mail REG_DWORD: MaxAttachmentMenuItems Value: 0 (no files) to 20 (Maximum)
This ready-to-use registry file sets the value to 6. You can edit the file in Notepad and change the value before adding it to the registry,
If you want to limit the number of Recent items you see on the Open sidebar in Word, Excel, or PowerPoint, look for the option in those programs at File > Options > Advanced. Show this number of Recent Documents is under the Display section. The maximum value here is 50.