Saving mail messages to the new default that you have specified is just like saving mail to the Folders directory. To save mail, do the following:
Type the file name, or a subdirectory name and then the file name, on the text field in the Mail Tool base window.
Note that if you have changed the default location to your home directory there is no need to type a tilde to specify your home directory as the destination.
Click SELECT on the message you want to save.
Choose Move or Copy.
The chosen mail message is saved to the directory name of your choice under your home directory (e.g. the directory name you substituted for Folders, the top level of your home directory, or a specified subdirectory).