Base: http://descolada.dartmouth.edu/mutt/patch-1.5.4+-ow.smime-encrypt-self.2
--- crypt.c	7 Mar 2003 08:23:27 -0000	3.17
+++ crypt.c	7 May 2003 14:57:00 -0000
@@ -246,8 +246,18 @@
     if ((WithCrypto & APPLICATION_SMIME)
         && (msg->security & APPLICATION_SMIME))
     {
-      if (!(tmp_pbody = crypt_smime_build_smime_entity (tmp_smime_pbody,
-                                                        keylist)))
+	   char *new_keylist = keylist;
+
+		 if (SmimeDefaultKey && query_quadoption(OPT_SMIMEENCRYPTSELF, _("Encrypt message to S/MIME Default Key also?")) == M_YES)
+		 {
+			int size = mutt_strlen(keylist) + mutt_strlen (SmimeDefaultKey) + 2; /* +1 for NULL, +1 for \n */
+			new_keylist = safe_malloc(size);
+			snprintf(new_keylist, size, "%s%s\n", keylist, SmimeDefaultKey);
+	   }
+		 
+	  tmp_pbody = crypt_smime_build_smime_entity (tmp_smime_pbody, new_keylist);
+	  safe_free((void **)&new_keylist);
+	  if (!tmp_pbody)
       {
 	/* signed ? free it! */
 	return (-1);
--- init.h.orig	2015-09-10 09:06:48.000000000 +0200
+++ init.h	2015-09-10 09:08:24.000000000 +0200
@@ -2748,6 +2748,11 @@
   ** possible \fCprintf(3)\fP-like sequences.
   ** (S/MIME only)
   */
+  { "smime_encrypt_self",	DT_QUAD,	 R_NONE, OPT_SMIMEENCRYPTSELF, 1 },
+  /*
+  ** .pp
+  ** Encrypt the message to smime_default_key too.
+  */
   { "smime_encrypt_with",	DT_STR,	 R_NONE, UL &SmimeCryptAlg, UL "aes256" },
   /*
   ** .pp
diff -u -d -b -B -r3.18 mutt.h
--- mutt.h.orig	Thu Nov  6 08:15:51 2003
+++ mutt.h	Thu Nov  6 08:16:43 2003
@@ -275,6 +275,7 @@
   OPT_DELETE,
   OPT_FORWEDIT,
   OPT_INCLUDE,
+  OPT_SMIMEENCRYPTSELF,
   OPT_MFUPTO,
   OPT_MIMEFWD,
   OPT_MIMEFWDREST,
--- contrib/smime.rc.orig	2015-08-30 19:06:38.000000000 +0200
+++ contrib/smime.rc	2015-09-10 09:14:20.000000000 +0200
@@ -23,8 +23,12 @@
 
 # The (default) keyfile for signing/decrypting.  Uncomment the following
 # line and replace the keyid with your own.
-set smime_default_key="12345678.0"
+# set smime_default_key="12345678.0"
 
+# Uncomment the following line in addition to the one above, if you want that
+# all encrypted messages are also encrypted with your default key.
+# set smime_encrypt_self = yes
+  
 # Uncomment to make mutt ask what key to use when trying to decrypt a message.
 # It will use the default key above (if that was set) else.
 # unset smime_decrypt_use_default_key