Just noticed this in passing & thought I'd mention it.
Index: starttls.8
===================================================================
RCS file: /cvs/src/share/man/man8/starttls.8,v
retrieving revision 1.22
diff -u -p -r1.22 starttls.8
--- starttls.8 24 Dec 2015 16:54:37 -0000 1.22
+++ starttls.8 22 Jun 2017 13:23:48 -0000
@@ -256,7 +256,7 @@ therefore still of value even with TLS a
.Pp
Because TLS can only authenticate at the server level, true
end-to-end authentication of the mail message cannot be performed with
-only the use of STARTLS on the server.
+only the use of STARTTLS on the server.
The use of S/MIME or PGP email and trustworthy key hierarchies can guarantee
full confidentiality and integrity of the entire message path.
.Pp
