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Zimbra Spam & Email Filters

Zimbra Spam & Email Filters

The Information Technology Department has devised several means for combatting spam emails. These are listed below.

There are two levels of Spam protection which the College of New Jersey provides:

  1. When mail is received, the sender’s address is checked against a few RBLs, lists of known spammers, and the message is immediately rejected if the address is on a list.
  2. After passing the first check, the message is scored with SpamAssassin, which scans the message for information commonly found in spam.

 

So what does SpamAssassin do? SpamAssassin runs numerous tests to identify unsolicited email. Each test will add or subtract from the total score. A positive score means the message is more likely to be spam.  Mail with a score of 15 or higher is automatically discarded, and mail with a score of between 6 and 15 is sent to the Junk folder.  Information is added to the message about which tests SpamAssasin used to score the message.  This information can be seen in the raw text of the email. To view this information in Zimbra, right click on the message and go to “Show Original”.  At the top of the message, X-Spam-Score is the total score SpamAssassin assigned to the email. X-Spam-Level represents the score with stars (*) instead of a number, which is helpful for additional spam filtering. Lastly, “X-Spam-Status” shows the individual tests used to score the message.

If you wish to provide your own spam protection, on top of that which the college provides, please take a look at the following. You can chose any, or all of these options.

A “Better” Zimbra Spam Filter Due to the fact that this spam filter is more powerful, some users may mistakenly find certain “non spam” emails marked as Junk.  If you find this to be a problem, you can add a “*” to the first condition of the filter.  The more stars added, the less powerful the filter will become.  The stars represent the spam score in spamassassin. 20 is the highest you can get and we drop messages with a score of 15 or higher and mark messages as spam with a score greater than six. SpamAssassin checks each messages with numerous tests that each add or subtract from the score. Please also note that since the campus default is 6 stars, “******”,  you will not need to filter higher than this.
Filtering “Bounced” Emails Many users have noticed that they are receiving a high number of emails that claim to be bounce-back emails. That is: the messages you would received if you sent an email to an incorrect address. Generally, these are not bouce-backs from emails you’ve sent. There are people out there who do what’s called “spoofing”, where they send tons of email out, and use your email address as the return address. Thus, if the email is undeliverable for some reason, you get the bounce-back instead of the actual sender. This filter looks for the BOUNCE_MESSAGE test in SpamAssassin, which only off-campus emails would have. Legitimate bounce messages (which you could get) will not have this tag, and will therefore show up (as they should) in your inbox. Note: we recommend that if you use this filter, you check your Junk folder every couple of days, just to make sure that legitimate bounce messages aren’t getting marked as junk.
A Calendar Spam Filter Some users have complained that they are getting spam emails that are calendar/meeting requests, and the events are getting added to their calendars. This filter discards any message with a calendar/meeting attachment that is not from a .edu domain, or from someone in your address book. We recommend that this one be used with caution, because it automatically discards emails, rather than filing them into junk or trash. The reason we opted to go this route is that moving messages to junk or trash can still cause the meeting to show up on your calendar.
Build Your Own Filter If none of these filters is exactly what you need, the Zimbra Mail Filters system under “Options” is extremely versatile, and will allow you to create a number of custom filters, each one designed to your own specifications.
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