Header Behavior in conf.c

The sendmail program has a built-in understanding of many header names. How those names are used is determined by a set of flags in the source file conf.c supplied with the source distribution. Site policy determines which flags are applied to which headers, but in general, conf.c applies them in the way that is best suited for almost all Internet sites. If you desire to redefine the flags for a particular header name, look for the name’s declaration in the C-language structure definition HdrInfo in conf.c. Be sure to read the comments in that file. Changes to header flags represent a permanent site policy change and should not be undertaken lightly. (We illustrate this process after explaining the flags.)

The flags that determine header use are listed in Table 25-3. Note that each flag name is prefixed with an H_.

Table 25-3. Header flags in conf.c






Section 25.6.1

V5 and above

Always process ?flags?


Section 25.6.2

V8.7 and above

Strip value from header


Section 25.6.3

V8.10 and above

Expand macros only at time of delivery


Section 25.6.4

V5 and above

Process ?flags?


Section 25.6.5

V8.7 and above

Is “content transfer encoding”


Section 25.6.6

V8.7 and above

Is “content type”


Section 25.6.7

V5 and above

If already in headers, don’t insert


Section 25.6.8

V8.8 and above

Field can be RFC2047-encoded


Section 25.6.9

V5 and ...

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.