Remove USE_GROFF since mandoc -Tlint -Werror *.{1,5} is happy, and the manpages render fine with mandoc. (see http://www.openbsd.org/faq/ports/specialtopics.html#Mandoc for ref)
extsmail enables the robust sending of e-mail to external commands. In effect extsmail masquerades as the standard UNIX sendmail program, reading messages, and later trying to send them by user-defined commands.