libmilter-dev 8.15.2-9ubuntu1 (i386 binary) in ubuntu bionic

 The Sendmail Mail Filter API (Milter) is designed to allow third-party
 programs access to mail messages as they are being processed in order
 to filter meta-information (headers) and content.
 .
 The Debian Sendmail package is built to support libmilter.
 .
 This is the libmilter static library and include files for development.
 .
 The documentation on building a Milter is in the sendmail-doc package.