Compiling and Installing Your Filter
To compile a filter, modify the Makefile provided with the sample program, or:
- Put the include and Sendmail directories in your include path (e.g. -I/path/to/include -I/path/to/sendmail).
- Make sure libmilter.a is in your library path, and link your application with it (e.g. "-lmilter").
- Compile with pthreads, either by using -pthread for gcc, or linking with a pthreads support library (-lpthread).
Your compile command line will look like
cc -I/path/to/include -I/path/to/sendmail -c myfile.c
and your linking command line will look something like
cc -o myfilter [object-files] -L[library-location] -lmilter -pthread
If you use a sendmail version older than 8.13 please see the instructions for your version. The default compilation options for sendmail enable support for milters since 8.13.
Next, you must add the desired filters to your sendmail configuration
Mail filters have three equates:
S= equate specifies the socket where
sendmail should look for the filter; the optional
T= equates specify flags and timeouts, respectively.
All equates names, equate field names, and flag values are case sensitive.
The current flags (
|R||Reject connection if filter unavailable|
|T||Temporary fail connection if filter unavailable|
If a filter is unavailable or unresponsive and no flags have been specified, the MTA will continue normal handling of the current connection. The MTA will try to contact the filter again on each new connection.
There are three fields inside of the
T= equate: S, R, and E.
Note the separator between each is a ";" (semicolon), as ","
(comma) already separates equates.
The value of each field is a decimal number followed by a single letter designating the units ("s" for seconds, "m" for minutes). The fields have the following meanings:
|C||Timeout for connecting to a filter. If set to 0, the
|S||Timeout for sending information from the MTA to a filter. Default: 10s|
|R||Timeout for reading reply from the filter. Default: 10s|
|E||Overall timeout between sending end-of-message to filter and waiting for the final acknowledgment. Default: 5m|
The following sendmail.mc example specifies three filters. The first two rendezvous on Unix-domain sockets in the /var/run directory; the third uses an IP socket on port 999.
INPUT_MAIL_FILTER(`filter1', `S=unix:/var/run/f1.sock, F=R') INPUT_MAIL_FILTER(`filter2', `S=unix:/var/run/f2.sock, F=T, T=S:1s;R:1s;E:5m') INPUT_MAIL_FILTER(`filter3', `S=inet:999@localhost, T=C:2m') define(`confINPUT_MAIL_FILTERS', `filter2,filter1,filter3') m4 ../m4/cf.m4 myconfig.mc > myconfig.cf
By default, the filters would be run in the order declared,
i.e. "filter1, filter2, filter3"; however, since
confINPUT_MAIL_FILTERS is defined, the filters will be
run "filter2, filter1, filter3".
Also note that a filter can be defined
without adding it to the input filter list by using
MAIL_FILTER() instead of INPUT_MAIL_FILTER().
The above macros will result in the following lines being added to your .cf file:
Xfilter1, S=unix:/var/run/f1.sock, F=R Xfilter2, S=unix:/var/run/f2.sock, F=T, T=S:1s;R:1s;E:5m Xfilter3, S=inet:999@localhost, T=C:2m O InputMailFilters=filter2,filter1,filter3
Finally, the sendmail macros accessible via smfi_getsymval can be configured by defining the following m4 variables (or cf options):
|In .mc file||In .cf file||Default Value|
For information about available macros and their meanings, please consult the sendmail documentation.