A quick guide on the proper way to share Dropbox folders.
1. Next to the folder you wish to share, click the Share button.
2. Click the Send link... option.
3. Click the Change Permissions / add expiration link.
4. Select the Only people with the password bullet, and enter a password for the folder.
(Remember this password, you will need it later.)
5. Click Yes and set an expiration date. Then click Save settings.
6. Highlight the link to the folder, and copy it. (DO NOT use the "Send this link to" option.)
7. Open your email, and paste the link you copied in Step 6. Make sure to also send the password you selected in Step 4. (BCC the recipients, DO NOT enter them in the "To:" line.)
