diff -uprN nail/sendout.c nail-patched/sendout.c
--- nail/sendout.c	2015-07-16 14:15:22.864905226 +0200
+++ nail-patched/sendout.c	2015-07-17 09:41:06.778677181 +0200
@@ -966,6 +966,19 @@ mail1(struct header *hp, int printheader
 		return STOP;
 	}
 #endif
+
+	/*
+	 * Variable "from" is set but empty, let user know
+	 * that something is wrong.
+	 */
+	if ((cp = value("from")) != NULL && !*cp) {
+		fprintf(stderr, "From address is empty. ");
+		fprintf(stderr, "Check your mail config ");
+		fprintf(stderr, "file for typos. E.g. no ");
+		fprintf(stderr, "whitespace after set from=");
+		fprintf(stderr, "\n");
+	}
+
 	if ((cp = value("autocc")) != NULL && *cp)
 		hp->h_cc = cat(hp->h_cc, checkaddrs(sextract(cp, GCC|GFULL)));
 	if ((cp = value("autobcc")) != NULL && *cp)
diff -uprN nail/smtp.c nail-patched/smtp.c
--- nail/smtp.c	2015-07-16 14:15:17.626914449 +0200
+++ nail-patched/smtp.c	2015-07-17 09:17:43.412730513 +0200
@@ -135,7 +135,7 @@ myaddrs(struct header *hp)
 		if (hp->h_from->n_name)
 			return savestr(hp->h_from->n_name);
 	}
-	if ((cp = value("from")) != NULL)
+	if ((cp = value("from")) != NULL && *cp)
 		return cp;
 	/*
 	 * When invoking sendmail directly, it's its task
@@ -177,6 +177,9 @@ smtp_auth_var(const char *type, const ch
 	char	*var, *cp;
 	int	len;
 
+	if (type == NULL || addr == NULL)
+		return NULL;
+
 	var = ac_alloc(len = strlen(type) + strlen(addr) + 7);
 	snprintf(var, len, "smtp-auth%s-%s", type, addr);
 	if ((cp = value(var)) != NULL)