Using SpamAssassin Tags to Filter your Mail -- Advanced topics
Changing the filtering threshold
Changing other behaviors of SpamAssassin
Fine-tuning your
filtering
Server-side filtering ("procmail")
as the alternative to client-side rules
Changing the filtering threshold
You can change the value of yourspam_threshold by logging in to your online directory entry. If you find that a lot of spam is not being tagged, or that too much legitimate mail is being tagged erroneously, you may want to modify your spam_threshold value. (Viewing the full headers of messages may help you to determine the best setting for you.) For example, values approaching 3.0 will almost certainly tag some of your legitimate mail as spam, while values approaching 9.0 will tag almost nothing (allowing too many spam messages to get through). By default the threshold has been set for you at 5.
Changing other default behaviors of SpamAssassin
You can also change other default values in your online directory entry. You can opt out of scanning entirely by specifying "no tagging", or you can specify that the Subject line of suspected spam be tagged in addition to the default extra header line. Subject line tagging may be useful if your mail client cannot filter on extra header lines. Subject line tagging will allow you to sort messages so that those suspected of being spam are grouped together where you can more easily inspect and delete them. You can also change the defaults for the text used in Subject line tagging and the character used to indicate the score in the "bar graphs."
The following fields can be modified:
| Field name | Description and possible values |
| spam_tag | Type of tagging SpamAssassin should use. The default value is "Extra header lines". Other choices are "Extra header and subject lines" and "No tagging". |
| spam_subject_prefix | Prefix to use in Subject line if spam_tag is set to "Extra header and subject lines" and the SpamAssassin score equals or exceeds the threshold. The default value is "Score". |
| spam_tag_character | The character use to indicate the score in the "bar graph." The default is an asterisk, "*". |
| spam_threshold | Messages whose scores equal or exceed the threshold are considered suspect and are tagged with a second extra header line: X-Score-High: YES. If spam_tag is set to "Extra header and subject lines", the Subject line of such messages will also be tagged. The default value is 5.0. Most people will find that the best value is somewhere between 3.5 and 5.5. |
Fine-tuning your filtering
As you begin to see the impact of filtering on your incoming mail, you may find that getting just the right filtering scheme can take some trial and error. Some of the mail that gets tagged as spam is actually mail you will want, especially if you subscribe to mailing lists. Some mail you don't want will still get through. When this occurs, you have a few choices. If you find that it happens too much, you may want to raise or lower your filtering threshold (as mentioned above) at www.bu.edu/directory/change-entry.html. However, if you find that the threshold is mostly error-free, and just needs a little fine-tuning, you may then want to build specific whitelist or blacklist filters.
Whitelist is a term that refers to the individualized filters you build to protect specific mail. Blacklist is a term that refers to the filters you create to indicate that a message is unwanted, even if it has not been identified as spam by SpamAssassin. To learn how to filter in this context, you can follow these instructions. In the case of whitelist items, each whitelist filter you build must come in sequence *before* the filter that contains X-Score-High: YES. (By default, newly-created filters do come first, so this should happen automatically. However, you can always manage the sequence of filtering using your mail program's interface for filter management.)
Note that these filters are stored locally (on your computer). If you use more than one computer to read your mail, you must set up these filters on each computer you use.