The splitmail program, used by metasend and mailto, expects
sendmail to be located in /usr/lib/sendmail, not
/usr/sbin/sendmail. Thsi works with out-of-the-box RedHat,
but may not if changes are done to the MTA.
Fixed in metamail-2.7-21, will be in next release. There were
actually quite a few instances of /usr/lib/sendmail throughout
metamail, but I think I got them all.