Mail::SpamAssassin::Plugin::MIMEEval(3)

has_check_for_ascii_text_illegal
    Adds capability check for "if can()" for check_for_ascii_text_illegal

check_for_ascii_text_illegal
    If a MIME part claims to be text/plain or text/plain;charset=us-ascii and the Content-Transfer-Encoding is 7bit (either explicitly or by default), then we should enforce the actual text being only TAB, NL, SPACE through TILDE, i.e. all 7bit characters excluding NO-WS-CTL (per RFC-2822).

    All mainstream MTA's get this right.

has_check_abundant_unicode_ratio
    Adds capability check for "if can()" for check_abundant_unicode_ratio

check_abundant_unicode_ratio
    A MIME part claiming to be text/plain and containing Unicode characters must be encoded as quoted-printable or base64, or use UTF data coding (typically with 8bit encoding). Any message in 7bit or 8bit encoding containing (HTML) Unicode entities will not render them as Unicode, but literally.

    Thus a few such sequences might occur on a mailing list of developers discussing such characters, but a message with a high density of such characters is likely spam.

has_check_qp_ratio
    Adds capability check for "if can()" for check_qp_ratio

check_qp_ratio
    Takes a min ratio to use in eval to see if there is an spamminess to the ratio of quoted printable to total bytes in an email.