oops.. msg->opt_fields are not filled, because stringpair_list_add() is strange. Fixed. "Received" headers are discarded explicitly, so they DON'T GO into msg->opt_fields, as desired for privacy reasons.

src/headerparser.cc

@@ -45,6 +45,14 @@ struct ParserBase
 };
 
 
+struct Discard : public ParserBase
+{
+	virtual void assign(message* msg, const std::string& s) override
+	{
+		// Do nothing, intentionally. So this header is discarded.
+	}
+};
+
 // Parser that assigns the result of the function to the message data member
 template<class T>
 struct TParser : public ParserBase
@@ -130,6 +138,7 @@ const std::map<std::string, struct ParserBase*> parsers =
         {"In-Reply-To", P<DS, stringlist_t*>(&message::in_reply_to, message_id_list, &create_stringlist) },
         {"References" , P<std::vector<std::string>, stringlist_t*>(&message::references, message_id_list, &create_stringlist) },
         
+        {"Received", new Discard },
     };
 
 // parses the header and fill the parts in msg
@@ -143,9 +152,25 @@ void parse_header(message* msg, const HeaderSection& header)
         const auto p = parsers.find( h.name );
         if(p == parsers.end())
         {
-            // unknown header with no special parser:
-            stringpair_list_add( msg->opt_fields, new_stringpair( h.name.c_str(), h.value.c_str() ));
+            // unknown header with no special parser: just dump it in opt_fields
+            auto sp = new_stringpair( h.name.c_str(), h.value.c_str() );
+            auto f = stringpair_list_add( msg->opt_fields, sp);
+            
+            // the function above has a strange semantic:
+            // it adds the stringpair to the given list (if it is non-NULL) or returns it (if given list is NULL).
+            if(f)
+            {
+                if(msg->opt_fields == nullptr) 
+                {
+                    msg->opt_fields = f;
+                }else{
+                    // do nothing. f is already added to the list. oO
+                }
+            }else{ // stringpair_list_add() fails for whatever reason: avoid memory leak
+                free_stringpair(sp);
+            }
         }else{
+            // do the "right thing" with this well-known header line:
             p->second->assign(msg, h.value);
         }
     }

src/unittest_mime.cc

@@ -20,6 +20,7 @@ namespace std
 	
 }
 
+using namespace std::string_literals;
 
 namespace {
 	static const char* mail1_eml =
@@ -147,7 +148,7 @@ std::string out(stringlist_t* sl)
 {
 	if(sl==nullptr)
 	{
-		return "SL[] ";
+		return "NULL ";
 	}else{
 		std::string ret = "SL[";
 		char* s = sl->value;
@@ -163,6 +164,26 @@ std::string out(stringlist_t* sl)
 }
 
 
+std::string out(stringpair_list_t* spl)
+{
+	if(spl==nullptr)
+	{
+		return "NULL ";
+	}else{
+		std::string ret = "SPL[";
+		auto sp = spl->value;
+		ret += "“"s + sp->key + "”:“"s + sp->value + "”";
+		while(spl->next)
+		{
+			spl = spl->next;
+			auto sp = spl->value;
+			ret += ", “"s + sp->key + "”:“"s + sp->value + "”";
+		}
+		return ret + ']';
+	}
+
+}
+
 #define PRINT(member)  std::cerr << "\t" #member ": " << out(m->member) << "\n"
 
 void print_message(message* m)