Knowledgebase

Managing Spam With Zimbra Filters

Zimbra uses an anti-spam filter called SpamAssassin to greatly reduce the amount of spam reaching your inbox. The default spam filtering is adequate for many users. However, if you receive too much spam in your in-box or find legitimate messages are being sent to your Junk folder you may wish to delve a litter deeper in to Zimbra spam filtering.

There are three ways to filter email in Zimbra.

1. The "Spam" and "Not Spam" buttons allow you to manually flagged messages as Spam or Not Spam.
2. The Junk Filtering Zimlet (available to Premium accounts only) allows customizing the level of automatic filtering by SpamAssassin.
3. Zimbra custom filters provide a way to "Whitelist" known good mail senders.

Spam/Not Spam

When logged-in to Zimbra Webmail you'll notice the "Spam" button when viewing your email. You should mark messages as Spam by clicking the check box next to all Spam messages and then clicking the "Spam" button. When you mark a message as Spam by clicking the "Spam" button it will be flagged, moved to your Junk folder and reported as Spam for system wide filtering purposes. Simply deleting such messages will not help reduce Spam in the future.

When you see a legitimate email has been flagged as Spam and moved to the Junk folder, view that message and click the "Not Spam" button. That message will be moved to your Inbox. If you click "Not Spam" by mistake, you can just click the "Spam" button again on that message to re-flag it as Spam and move it back to your Junk folder.

Marking messages as Spam or Not Spam by clicking the Spam or Not Spam buttons helps SpamAssassin learn and get better over time. Since SpamAssassin watches the Junk folder, you should never delete messages from the Junk folder. SpamAssassin will delete messages from the junk folder automatically when they are no longer needed.

Junk Filtering Zimlet (Premium accounts only)

Zimbra Premium accounts can control the level of filtering provided by SpamAssassin with our custom Junk filtering zimlet. Four levels of filtering are offered by the Junk Filter zimlet.

• Low - Default level of spam filtering (Spam score 8 or higher)
• High - Stricter level of spam filtering (Spam score 5 or higher)
• Disabled - No spam filtering
• Custom - User-defined spam filtering

When mail is filtered, it will go into your Junk folder.

To change the filtering level, log into Zimbra Webmail, click the "Preferences" button, click the "Junk Filter" button, then select your preferred filtering level. The High level of filtering is the most aggressive, filtering email with a Spam Assassin score of 5 or higher so if you select that filter you'll likely want to keep a closer eye on your Junk folder since there will likely be more legitimate messages flagged as spam. The Low level filter is less aggressive, filtering email with a Spam Assassin score of 8 or higher. While you're less likely to filter legitimate email with this level of filtering it is still a good idea to watch the Junk folder to be sure you don't miss any important email which may be getting a higher Spam Assassin score than expected. Selecting the Disable button will turn all filtering off so no email is sent to your Junk folder at all. We recommend the Disable option only if you use an email client like Thunderbird and manage your own filtering through that software. Custom allows you to enter a number from 1-10 to fine tune the filtering level. Lower numbers are more strict, higher numbers are less strict.

Advanced Zimbra Filtering with a Custom Whitelist

Zimbra allows the creation of custom filters which can be used for a variety of purposes. "Whitelisting" known good email senders is a popular use of Zimbra custom filters.

To create a custom Zimbra Whitelist filter.

1. Log into Zimbra Webmail then select Preferences, then Filters.
2. Click the "Create Filter" button.
3. Enter "Whitelist" in the Filter Name field.
4. Set the filter rule to say: If "any" of the following conditions are met:
5. Change "Subject" to "From"
6. Change "contains" to "matches exactly"
7. Enter an email address you want to whitelist.
8. Click the green "+" for each additional address you wish to add.
9. Ensure "Perform the following actions:" says "Keep in inbox".
10. Ensure the "Do not process additional filters" box is checked.
11. Click the "Ok" button when finished

The new filter will automatically be added at the top of your filter list. As you add additional filters you will want to be sure that you keep using the "Move Up" feature to keep it at the top of your filter rules so it is processed before any other filters. This will help you keep a high level of filtering while ensuring any mail that might be getting sent to the Junk folder can be saved to your inbox prior to other filters being applied.