Here is an approach that should work in most versions of Horde (webmail). Note that if your folders contain a large amount of email you will probably need to divide them into smaller folders.
Exporting Your Emails from Horde
1: In the navigation menu at left click on your general "mail" folder (which should contain all your mail sub-folders)
2: Next, in the menu bar at top, click on "Folders."
3: Now select the folder you wish to export by checking its box.
4: Next, select "Download Folder(s)" from the "Choose Action:" drop-down box.
5: You will be given an .mbox file to download. Store it in a location you'll remember.
Importing Your Emails Into Horde
1: Click "Folders" in the menu bar.
2: Select "Create Folder" from the "Choose Action:" drop-down box and give your new folder a name (preferrably the same name as the one you just exported from).
3: Now select this folder by checking its box.
4: This time, select "Import Messages" from the "Choose Action:" drop-down box.
5: Next you'll browse to the download location you used above and select your .mbox file to import and click "Import."
6: Your messages should automatically be imported into your newly created folder.
7: Double check the new folder and make sure the messages are there and that they are intact.
For folders that are too large (your browser stalls or stops loading on export), you most likely have messages with attachments that are too large to handle. I recommend sorting the messages by size, downloading the attachments from the largest messages and forwarding them on with your preferred email client along with the message body. Then move (or delete) these messages from the folder you wish to export and try again. Eventually you will have gotten the folder down to a reasonable enough size and the export will succeed.
How to use folders to make backing up and deleting easier
When you create a backup you can't view the emails contained in the backup file as they are in an archive format. You can import this archive back in to Horde and then view them. By organising your Inbox with folders it makes life easier when the need arises to make backups or delete large numbers of emails.
1: Select the emails you want to move or copy by ticking the box on the left hand side next to each message
2: Where it says "Move/Copy - with the drop down box next to it, click on either "Move or Copy" then select "New Folder" from the drop down box
3: Give the folder a name and it will either move or copy the selected emails to this new folder
4: Now when you select Folders from the menu bar at the top of the screen you will see this new folder has been created.
5: You can now back up this folder in the same way as described earlier or even delete it and all its contents.
Posted by Tony