The program lies within System Tools, more precisely General. This free Mac app was originally created by Glenn Anderson.
From the developer:
eimsmail is a replacement for the sendmail command that uses EIMS to send. eimsmail will only work with the full version of EIMS.
eimsmail is intended to be parameter compatible with common versions of the sendmail command. Currently it supports the following parameters:
-B: specify the content encoding, 7BIT or 8BITMIME
-i: EOF is end of message, rather than a line with a "."