Made discard action log a message to avoid confusion about disappearing messages.

src/lib-sieve/cmd-discard.c

@@ -2,6 +2,7 @@
  */
 
 #include "lib.h"
+#include "str-sanitize.h"
 
 #include "sieve-common.h"
 #include "sieve-commands.h"
@@ -146,9 +147,12 @@ static void act_discard_print
 
 static bool act_discard_commit
 (const struct sieve_action *action ATTR_UNUSED, 
-	const struct sieve_action_exec_env *aenv ATTR_UNUSED, 
+	const struct sieve_action_exec_env *aenv, 
 	void *tr_context ATTR_UNUSED, bool *keep)
 {
+	sieve_result_log(aenv, 
+		"marked message to be discarded if not explicitly delivered "
+		"(discard action)");
 	*keep = FALSE;
 
 	return TRUE;