Moving your mail storage location - SeaMonkey
From MozillaZine Knowledge Base
By default, your mail is stored in your profile folder, along with your address books and settings. If you want to move your mail (but not the entire contents of the profile folder) to a different location, follow the steps below.
1. Exit your Mozilla Suite/SeaMonkey application if it is running. Create a folder in the new location where you would like to store your mail. If changing the storage location for more than one account, create a separate folder for each account.
2. Go to your existing profile folder and copy your mail files over to the new location. For each account you want to move: find that account's folder in the "Mail" folder (POP3 accounts) or the "ImapMail" folder (IMAP accounts) and copy its entire contents, including all of its subfolders, over to the new location.
3. Start Mozilla Suite/SeaMonkey and go to "Edit -> Mail & Newsgroup Account Settings -> [account name] Server Settings". Where it says "Local directory", click on the "Browse..." button to select the folder you created in step 1. Click the "OK" button and verify that the "Local directory" field shows the correct path to the new storage location of your mail.
4. If you have more than one mail account, repeat step 3 for each account whose mail you moved in steps 1-2.
You will need to restart the application to see the changes. Once you're certain that Mozilla Suite/SeaMonkey recognizes the new location of your mail, you can go back and delete the mail files from your profile folder.