MIME headers are special, in that they can appear both in the header
portion of a message and in the body of the message. Such headers
MIME-Version: (which can only appear in
the header portion),
Content-Type: (which can
appear in both), and
appears in both). All such headers have a name (the part to the left
of the colon) and a field (the part to the right of the colon). The
length of a MIME header is the combined length of these two parts.
In addition, some MIME headers can also have parameters following the value. For example:
Content-Type: image/gif; name="filename.gif"
Here, the value is everything up to and including the first semicolon. Each semicolon-delimited item that follows that value is a parameter. The following, for example, has one value and two parameters:
Content-Type: multipart/mixed; charset="Windows-1252"; boundary="----=_NextPart_000_00DC_01BEAC82.35D91E20"
Certain kinds of MUA attacks can be based on overly long MIME
headers. To prevent the success of such attacks, V8.10
sendmail has introduced the
MaxMimeHeaderLength option. It sets the maximum
length for both MIME headers and MIME header parameters. The forms of
MaxMimeHeaderLength option are as follows:
O MaxMimeHeaderLength=hdr/param ← configuration file (V8.10 and later) -OMaxMimeHeaderLength=hdr/param ← command line (V8.10 and later) define(`confMAX_MIME_HEADER_LENGTH',hdr/param)← mc configuration (V8.10 and later)
hdr is the ...