If you have a list of emails you would like to whitelist, you can copy and paste these to the server Whitelist Filter under Horde Mail Manager:
1. Log into Webmail: Go Here for instructions on how to log into WebMail
2. Make sure Horde is selected as your Mail Reader. If you are using RoundCube, simply Click On the WebMail CPanel Logo in the top right of your screen.
3. Click to Open Horde. When Horde loads, it usually defaults to your Inbox. Whatever screen it defaults to when it loads, on the Top Right of your screen you should see a Cog Icon, and when you mouse over it, a sub-menu with Preferences as a selection should appear. Mouse over the Menu Selection "Preferences", and you will see another sub menu titled "Mail". Click on Mail to go to the next screen.
4. Once you are in the Preferences for Mail Screen, the first column should show the choice "Filters". Click on this for the Filters Screen.
5. Once this page loads, you should see "Edit Your Whitelist" and "Edit Your Blacklist". Click on either, depending on whether you are blocking an email address (Black List) or allowing an Email Address (White List).
6. (Example White List). Once you are in the White List Filter Screen, you will see a Box titled Whitelist Addresses. This is where you can copy and paste the addresses you wish to allow your email server to send to without bouncing. Type or Paste an email per line and click the Save button once you are finished.
It is encouraged that you also contact the recipient and ask them to White List or allow your email address to send and receive from their server as well.