When a mail message is converted from 8 to 7 bits (see the EightBitMode option in EightBitMode), it is important that the result look like a MIME message. V8.7 and later sendmail first outputs the following header if one is not already present:

MIME-Version: 1.0

After that, sendmail looks for a Content-Type: header (Content-Type:). If none is found, the following is inserted, where dfltchset is the value declared for this option:

Content-Type: text/plain; charset=dfltchset

The forms of the DefaultCharSet option are as follows:

O DefaultCharSet=dfltchset               configuration file (V8.7 and later) 
-ODefaultCharSet=dfltchset               command line (V8.7 and later) 
define(`confDEF_CHAR_SET',dfltchset) mc configuration (V8.7 and later) 

If the DefaultCharSet option is undefined, dfltchset defaults to the string unknown-8bit. The default for the mc technique is to omit this option.

Note that if the C= equate (C=) is present for the sender’s delivery agent, that character set supersedes this DefaultCharSet.

The DefaultCharSet option is safe. If specified from the command line, sendmail will not relinquish its special privileges.

Get Sendmail, 3rd Edition now with O’Reilly online learning.

O’Reilly members experience live online training, plus books, videos, and digital content from 200+ publishers.