diff -urN busybox-1.32.0.orig/mailutils/sendmail.c busybox-1.32.0/mailutils/sendmail.c
--- busybox-1.32.0.orig/mailutils/sendmail.c	2020-06-26 20:47:44.000000000 +0200
+++ busybox-1.32.0/mailutils/sendmail.c	2021-01-05 09:04:05.973347132 +0100
@@ -271,7 +271,7 @@
 	// -a is for ssmtp (http://downloads.openwrt.org/people/nico/man/man8/ssmtp.8.html) compatibility,
 	// it is still under development.
 	opts = getopt32(argv, "^"
-			"tf:o:iw:+H:S:a:*:v"
+			"tf:o:iw:+H:S:a:*:vF:"
 			"\0"
 			// -v is a counter, -H and -S are mutually exclusive, -a is a list
 			"vv:H--S:S--H",