Here are the steps:
1. Click Search for a case
2. Click the Clear button
3. Check the Primary Names Only
4. Enter O for the status to only search for Open Cases or leave blank for all cases.
5. Click the Right arrow at the lower right corner and select Has Email
6. Click the Search By and change it to Last Name (instead of Last Name quick so the search runs faster)
7. Click Search and then click Yes to continue.
8. Click the second button at the far lower left to Export out to a File.
9. Select the Email to Clipboard option and click Proceed.
In your Email program, type Ctrl-V to Paste all the Emails.
IMPORTANT: It's strongly recommended to send the Email to yourself and Paste the Emails into the Blind Copy section for privacy. Do not paste the Emails into the cc (be sure to use the bcc / blind copy option).