fix #4546

public/language/en_GB/error.json

@@ -27,6 +27,7 @@
 	"no-email-to-confirm": "This forum requires email confirmation, please click here to enter an email",
 	"email-confirm-failed": "We could not confirm your email, please try again later.",
 	"confirm-email-already-sent": "Confirmation email already sent, please wait %1 minute(s) to send another one.",
+	"sendmail-not-found": "The sendmail executable could not be found, please ensure it is installed and executable by the user running NodeBB.",
 
 	"username-too-short": "Username too short",
 	"username-too-long": "Username too long",

src/emailer.js

@@ -113,7 +113,11 @@ var fallbackTransport;
 				}
 			}
 		], function (err) {
-			callback(err);
+			if (err && err.code === 'ENOENT') {
+				callback(new Error('[[error:sendmail-not-found]]'));
+			} else {
+				callback(err);
+			}
 		});
 	};