Thurman, nothurman, uma, nouma Channel Options

Convert some non-standard "attachments" to MIME format
The  channel option on a source channel causes the MTA to "sniff" incoming, non-MIME  messages and convert them to MIME format, in the process converting certain non-standard "attachment" formats (e.g.,  uuencoded or BinHex "blobs" embedded in messages) into MIME format attachments. While this may seem like a positive transformation to perform on messages, modifications of message content should always be a last resort, the resulting MIME-ification of messages has limitations and may be considered undesirable in some circumstances or to some users, this "sniffing" does incur processing overhead, and such an approach may appear as a deceptively "easy" fix for communicating with non-standard e-mail software (when a better, more permanent solution would be to upgrade the out-of-date, non-standard software that is emitting such "blobs"). As such, the  channel option is the default -- and any decision to configure with   should  be made with due consideration and caution.

The  source channel option is like , except that with  , the message "sniffing" and content transformation only occurs if the MTA was already performing message body processing (and hence would have been converting the message body to MIME format already), for instance cases of incoming non-MIME  messages that illegally contain unlabelled eight bit characters. is the default.

Note that    mapping table keywords exist to configure   or   type processing on a somewhat more selective basis.

The  or   processing on its own merely causes  "blobs" in non-MIME messages to get converted to fairly "generic" MIME parts, with Content-type of application/octet-stream and a Content-transfer-encoding of X-UUENCODE. Optionally, one may configure to guess (typically based on filename, especially filename extension) at a better Content-type labelling, and/or to convert to a different Content-transfer-encoding, using the MTA&#x27;s facility for Relabelling MIME header lines.

See also:
 * CHARSET-CONVERSION mapping table
 * Relabelling MIME header lines
 * Attachments and MIME processing channel options
 * Channel options