content/blog/mail_server_alpine_postfix_dovecot_tutorial/index.md: add line for adding SA headers with amavis

content/blog/mail_server_alpine_postfix_dovecot_tutorial/index.md

@@ -1719,6 +1719,15 @@ Enable spam filtering by setting `@bypass_spam_checks_maps` in your `/etc/amavis
     \%bypass_spam_checks, \@bypass_spam_checks_acl, $bypass_spam_checks_re);
 ```
 
+SpamAssassin gives us helpful email headers with a "spam score". By default, Amavis only adds these headers if the spam
+score is at least 2.0. To have the headers always be added, find and change (or add if it is not already there)
+
+```conf
+$sa_tag_level_deflt = undef;
+```
+
+If you only want SpamAssassin's headers at, say, 1.0, replace `undef` with `1.0`.
+
 Restart Amavis:
 
     # rc-service amavisd restart