Fix the Apple Mail Moving message error

In order to fix the "error occurred while moving messages to mailbox (null)" error you will need to assign severals in the Apple Mail client. The error often occurs when deleting messages while the Trash fodler has not been assigned in the Mac mail client. It can also occur when moving email between unassigned folders. The error appears in the client as follows:

In order to use these instructions, you will need to have added an email account into the Apple Mail client.

1. Login to the Apple Mail Client
2. 

   Scroll down to your newly added mail account. Click on the drop-arrow to see the Drafts, Sent, Junk, and Trash folders, then click on the Drafts folder to highlight it
3. 

   In the Menu at the top of the screen, click on Mailbox, then scroll down to Use This Mailbox As
4. 

   Click on "Drafts Mailbox" in the menu that appears to the right. This will assign the Drafts folder in the Apple mail client to the corresponding server folder.
5. Repeat this action for your Sent, Junk, and Trash folders. Make sure to click on the respective folder assignment so that your files are going to the right place.

Congratulations! This fixes the "error occurred while moving messages to mailbox" error.