Using the Spam Filter in Mozilla Thunderbird

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Cutting Just the Spam

Make sure the spam filter is enabled in Mozilla Thunderbird if you want it to help you keep your inbox clean. Mozilla Thunderbird, Netscape and Mozilla include highly efficient spam filters using Bayesian statistical analysis. After a bit of training, its spam detection rate is stellar while false positives are practically nonexistent. If you do not like spam in your Mozilla Thunderbird, Netscape or Mozilla Inbox, you should really turn the junk mail filter on.

Turn on the Spam Filter in Mozilla Thunderbird

To have Mozilla Thunderbird filter junk mail for you:

  1. Select Tools | Account Settings... (Windows and Mac) or Edit | Account Settings (Linux) from the menu in Mozilla Thunderbird.
    • ​You can also select Preferences | Account Settings from the Thunderbird (hamburger) menu.
  2. For each account you want to use Mozilla Thunderbird's spam filter:
    1. Go to the Junk Settings category under the desired account.
    2. Make sure Enable adaptive junk mail controls for this account is checked.
  3. Click OK.

Prevent Mozilla Thunderbird from Overriding External Spam Filters

To have Mozilla Thunderbird accept and use spam filtering scores created by a spam filter that analyzes messages before Thunderbird receives them (at the server, for example, or on your computer):

  1. Open the spam filter settings for the desired email account in Mozilla Thunderbird. (See above.)
  2. Make sure Trust junk mail headers set by: is checked under Selection.
  1. Select the spam filter used from the list that follows.
  2. Click OK.

What about Blocking Senders? Will that Help as Well?

In addition to employing a spam filter, Mozilla Thunderbird also lets you block individual email addresses (and domains), of course.

While this is a proper tool to avoid senders (or automated software installations perhaps) that keep sending emails in which you have no interest at all, blocking senders does little to fight spam.

Junk emails do not come from identifiably stable email addresses. If you block the email address from which one spam email seems to come, there will be no noticeable effect as no other spam email will ever come from the same address.

How Does the Mozilla Thunderbird Spam Filter Work Then?

The Bayesian analysis Mozilla Thunderbird does for spam filtering assigns a spam score to each word and other parts of an email; over time, it learns which words typically appear in junk email, and which appear mostly in good messages.

Turn on the Spam Filter in Mozilla or Netscape

To enable "junk mail controls" in Mozilla Thunderbird 1, Netscape or Mozilla:

  1. Select Tools | Junk Mail Controls... from the menu.
  2. Make sure the account you want to turn spam filtering on for is selected under Account:.
  3. Now make sure Enable junk mail controls is selected.
  4. Click OK.