Moving emails to local folders removes them from the email Server. This helps in cleaning up your email storage space and thus facilitates you to stay under the allocated space limit. Always keep in mind that messages which you move from the Server to a local folder will be accessible only from the system where the local folder resides. So, moving the mail messages to your local folders can prove to be an effective way to clean out your email account in the situation where you are unable to delete them.

Copying your email messages to your local folders actually helps in the retention of email messages on the email Server and thus, it does not have any effect on your disk space. Email messages that are being copied to your local folders will still remain accessible from anywhere, since they are still available be on the Server itself. However, the process of copying messages is not an effective method to clean out your email account if you are experiencing disk space issues.

Outlook Express to Outlook
Outlook Express to Outlook Converter Tool to Convert DBX to PST