I experienced this with CPanel's Exim after an auto-update (a Google of this error produces lots of complaints with few clear solutions). In this case I'll put the solution at the top.
Run /scripts/buildeximconf to rebuild the Exim config and it should be fine after that.
mail -vs "from test" email@example.com < .bash_history
cwd=/root 4 args: send-mail -i -v firstname.lastname@example.org