diff --git a/lib/message/mu-document.cc b/lib/message/mu-document.cc
index f0c230c5..3c43aa0f 100644
--- a/lib/message/mu-document.cc
+++ b/lib/message/mu-document.cc
@@ -19,6 +19,7 @@
 
 #include "mu-document.hh"
 #include "mu-message.hh"
+#include "utils/mu-sexp.hh"
 
 #include <cstdint>
 #include <glib.h>
@@ -30,11 +31,37 @@
 #include <string>
 #include <utils/mu-utils.hh>
 
+
 using namespace Mu;
 
 constexpr uint8_t SepaChar1 = 0xfe;
 constexpr uint8_t SepaChar2 = 0xff;
 
+
+const Xapian::Document&
+Document::xapian_document() const
+{
+	if (dirty_sexp_) {
+		xdoc_.set_data(sexp_.to_string());
+		dirty_sexp_ = false;
+	}
+	return xdoc_;
+}
+
+template<typename SexpType> void
+Document::put_prop(const std::string& pname, SexpType&& val)
+{
+	sexp_.put_props(pname, std::forward<SexpType>(val));
+	dirty_sexp_ = true;
+}
+
+template<typename SexpType> void
+Document::put_prop(const Field& field, SexpType&& val)
+{
+	put_prop(std::string(":") + std::string{field.name},
+		 std::forward<SexpType>(val));
+}
+
 static void
 add_search_term(Xapian::Document& doc, const Field& field, const std::string& val)
 {
@@ -57,12 +84,6 @@ add_search_term(Xapian::Document& doc, const Field& field, const std::string& va
 }
 
 
-static std::string
-make_prop_name(const Field& field)
-{
-	return ":" + std::string(field.name);
-}
-
 void
 Document::add(Field::Id id, const std::string& val)
 {
@@ -74,9 +95,9 @@ Document::add(Field::Id id, const std::string& val)
 	if (field.is_searchable())
 		add_search_term(xdoc_, field, val);
 
-	if (field.include_in_sexp())
-		sexp_list().add_prop(make_prop_name(field),
-				     Sexp::make_string(std::move(val)));
+	if (field.include_in_sexp()) {
+		put_prop(field, val);
+	}
 }
 
 void
@@ -95,11 +116,10 @@ Document::add(Field::Id id, const std::vector<std::string>& vals)
 				      add_search_term(xdoc_, field, val); });
 
 	if (field.include_in_sexp()) {
-		Sexp::List elms;
+		Sexp elms{};
 		for(auto&& val: vals)
-			elms.add(Sexp::make_string(val));
-		sexp_list().add_prop(make_prop_name(field),
-				     Sexp::make_list(std::move(elms)));
+			elms.add(val);
+		put_prop(field, std::move(elms));
 	}
 }
 
@@ -113,19 +133,16 @@ Document::string_vec_value(Field::Id field_id) const noexcept
 static Sexp
 make_contacts_sexp(const Contacts& contacts)
 {
-	Sexp::List clist;
+	Sexp contacts_sexp;
 
 	seq_for_each(contacts, [&](auto&& c) {
+		Sexp contact(":email"_sym, c.email);
 		if (!c.name.empty())
-			clist.add(Sexp::make_prop_list(
-					  ":name",  Sexp::make_string(c.name),
-					  ":email", Sexp::make_string(c.email)));
-		else
-			clist.add(Sexp::make_prop_list(
-					  ":email", Sexp::make_string(c.email)));
+			contact.add(":name"_sym, c.name);
+		contacts_sexp.add(std::move(contact));
 	});
 
-	return Sexp::make_list(std::move(clist));
+	return contacts_sexp;
 }
 
 void
@@ -168,9 +185,7 @@ Document::add(Field::Id id, const Contacts& contacts)
 		xdoc_.add_value(field.value_no(), join(cvec, SepaChar1));
 
 	if (field.include_in_sexp())
-		sexp_list().add_prop(make_prop_name(field),
-				     make_contacts_sexp(contacts));
-
+		put_prop(field, make_contacts_sexp(contacts));
 }
 
 Contacts
@@ -204,22 +219,19 @@ Document::contacts_value(Field::Id id) const noexcept
 void
 Document::add_extra_contacts(const std::string& propname, const Contacts& contacts)
 {
-	if (!contacts.empty())
-		sexp_list().add_prop(std::string{propname},
-				     make_contacts_sexp(contacts));
+	if (!contacts.empty()) {
+		put_prop(propname, make_contacts_sexp(contacts));
+		dirty_sexp_ = true;
+	}
 }
 
 
 static Sexp
 make_emacs_time_sexp(::time_t t)
 {
-	Sexp::List dlist;
-
-	dlist.add(Sexp::make_number(static_cast<unsigned>(t >> 16)));
-	dlist.add(Sexp::make_number(static_cast<unsigned>(t & 0xffff)));
-	dlist.add(Sexp::make_number(0));
-
-	return Sexp::make_list(std::move(dlist));
+	return Sexp().add(static_cast<unsigned>(t >> 16),
+			  static_cast<unsigned>(t & 0xffff),
+			  0);
 }
 
 void
@@ -231,7 +243,6 @@ Document::add(Field::Id id, int64_t val)
 	 * we comply, by storing a number a base-16 and prefixing with 'f' +
 	 * length; such that the strings are sorted in the numerical order.
 	 */
-
 	const auto field{field_from_id(id)};
 
 	if (field.is_value())
@@ -239,11 +250,9 @@ Document::add(Field::Id id, int64_t val)
 
 	if (field.include_in_sexp()) {
 		if (field.is_time_t())
-			sexp_list().add_prop(make_prop_name(field),
-					     make_emacs_time_sexp(val));
+			put_prop(field, make_emacs_time_sexp(val));
 		else
-			sexp_list().add_prop(make_prop_name(field),
-					     Sexp::make_number(val));
+			put_prop(field, val);
 	}
 }
 
@@ -265,8 +274,7 @@ Document::add(Priority prio)
 	xdoc_.add_boolean_term(field.xapian_term(to_char(prio)));
 
 	if (field.include_in_sexp())
-		sexp_list().add_prop(make_prop_name(field),
-				     Sexp::make_symbol_sv(priority_name(prio)));
+		put_prop(field, Sexp::Symbol(priority_name(prio)));
 }
 
 Priority
@@ -281,52 +289,21 @@ Document::add(Flags flags)
 {
 	constexpr auto field{field_from_id(Field::Id::Flags)};
 
-	Sexp::List flaglist;
+	Sexp flaglist;
 	xdoc_.add_value(field.value_no(), to_lexnum(static_cast<int64_t>(flags)));
 	flag_infos_for_each([&](auto&& flag_info) {
 		auto term=[&](){return field.xapian_term(flag_info.shortcut_lower());};
 		if (any_of(flag_info.flag & flags)) {
 			xdoc_.add_boolean_term(term());
-			flaglist.add(Sexp::make_symbol_sv(flag_info.name));
+			flaglist.add(Sexp::Symbol(flag_info.name));
 		}
 	});
 
 	if (field.include_in_sexp())
-		sexp_list().add_prop(make_prop_name(field),
-				     Sexp::make_list(std::move(flaglist)));
+		put_prop(field, std::move(flaglist));
 }
 
 
-Sexp::List&
-Document::sexp_list()
-{
-	/* perhaps we need get the sexp_ from the document first? */
-	if (sexp_list_.empty()) {
-		const auto str{xdoc_.get_data()};
-		if (!str.empty()) {
-			Sexp sexp{Sexp::make_parse(str)};
-			sexp_list_ = sexp.list();
-		}
-	}
-
-	return sexp_list_;
-}
-
-std::string
-Document::cached_sexp() const
-{
-	return xdoc_.get_data();
-}
-
-void
-Document::update_cached_sexp(void)
-{
-	if (sexp_list_.empty())
-		return; /* nothing to do; i.e. the exisiting sexp is still up to
-			 * date */
-	xdoc_.set_data(Sexp::make_list(Sexp::List{sexp_list()}).to_sexp_string());
-}
-
 Flags
 Document::flags_value() const noexcept
 {
@@ -364,7 +341,6 @@ Document::remove(Field::Id field_id)
 			}
 		}
 	});
-
 }
 
 
diff --git a/lib/message/mu-document.hh b/lib/message/mu-document.hh
index 9c923a19..4cfe2442 100644
--- a/lib/message/mu-document.hh
+++ b/lib/message/mu-document.hh
@@ -52,13 +52,23 @@ public:
 	 *
 	 * @param doc
 	 */
-	Document(const Xapian::Document& doc): xdoc_{doc} {}
+	Document(const Xapian::Document& doc): xdoc_{doc} {
+		if (auto&& s{Sexp::parse(xdoc_.get_data())}; s)
+			sexp_ = std::move(*s);
+	}
+
+	/**
+	 * DTOR
+	 */
+	~Document() {
+		xapian_document(); // for side-effect up updating sexp.
+	}
 
 	/**
 	 * Get a reference to the underlying Xapian document.
 	 *
 	 */
-	const Xapian::Document& xapian_document() const { return xdoc_; }
+	const Xapian::Document& xapian_document() const;
 
 	/**
 	 * Get the doc-id for this document
@@ -138,24 +148,12 @@ public:
 	void remove(Field::Id field_id);
 
 	/**
-	 * Update the cached sexp from the sexp_list_
-	 */
-	void update_cached_sexp();
-
-	/**
-	 * Get the cached s-expression
-	 *
-	 * @return a string
-	 */
-	std::string cached_sexp() const;
-
-	/**
-	 * Get the cached s-expressionl useful for changing
+	 * Get the cached s-expression useful for changing
 	 * it (call update_sexp_cache() when done)
 	 *
-	 * @return the cache s-expression
+	 * @return the cached s-expression
 	 */
-	Sexp::List& sexp_list();
+	const Sexp& sexp() const { return sexp_; }
 
 	/**
 	 * Generically adds an optional value, if set, to the document
@@ -184,6 +182,7 @@ public:
 			return xdoc_.get_value(field_from_id(field_id).value_no());
 		}, std::string{});
 	}
+
 	/**
 	 * Get a vec of string values.
 	 *
@@ -229,9 +228,13 @@ public:
 	Flags    flags_value() const noexcept;
 
 private:
-	Xapian::Document	xdoc_;
-	Sexp::List		sexp_list_;
+	template<typename SexpType> void put_prop(const Field& field, SexpType&& val);
+	template<typename SexpType> void put_prop(const std::string& pname, SexpType&& val);
 
+
+	mutable Xapian::Document	xdoc_;
+	Sexp				sexp_;
+	mutable bool			dirty_sexp_{};	/* xdoc's sexp is outdated */
 };
 
 } // namepace Mu
diff --git a/lib/message/mu-fields.hh b/lib/message/mu-fields.hh
index 22b486b5..2579a767 100644
--- a/lib/message/mu-fields.hh
+++ b/lib/message/mu-fields.hh
@@ -186,8 +186,8 @@ struct Field {
 	 *
 	 */
 
-	constexpr char xapian_prefix() const
-	{ /* xapian uses uppercase shortcuts; toupper is not constexpr */
+	constexpr char xapian_prefix() const {
+		/* xapian uses uppercase shortcuts; toupper is not constexpr */
 		return shortcut == 0 ? 0 : shortcut - ('a' - 'A');
 	}
 
@@ -542,5 +542,6 @@ Option<Field> field_from_number(size_t id)
 		return field_from_id(static_cast<Field::Id>(id));
 }
 
+
 } // namespace Mu
 #endif /* MU_FIELDS_HH__ */
diff --git a/lib/message/mu-message.cc b/lib/message/mu-message.cc
index a8ff0f5f..58102609 100644
--- a/lib/message/mu-message.cc
+++ b/lib/message/mu-message.cc
@@ -182,23 +182,16 @@ Message::docid() const
 }
 
 
-const Mu::Sexp::List&
-Message::to_sexp_list() const
+const Mu::Sexp&
+Message::sexp() const
 {
-	return priv_->doc.sexp_list();
-}
-
-void
-Message::update_cached_sexp()
-{
-	priv_->doc.update_cached_sexp();
+	return priv_->doc.sexp();
 }
 
 Result<void>
 Message::set_maildir(const std::string& maildir)
 {
 	/* sanity check a little bit */
-
 	if (maildir.empty() ||
 	    maildir.at(0) != '/' ||
 	    (maildir.size() > 1 && maildir.at(maildir.length()-1) == '/'))
diff --git a/lib/message/mu-message.hh b/lib/message/mu-message.hh
index 3f2e001b..615b5d8c 100644
--- a/lib/message/mu-message.hh
+++ b/lib/message/mu-message.hh
@@ -23,6 +23,8 @@
 #include <memory>
 #include <string>
 #include <vector>
+#include <iostream>
+
 #include "mu-contact.hh"
 #include "mu-priority.hh"
 #include "mu-flags.hh"
@@ -336,37 +338,17 @@ public:
 			.string_vec_value(Field::Id::Tags);
 	}
 
-	/**
-	 * Get the cached s-expression for this message, or {} if not available.
-	 *
-	 * @return sexp or empty.
-	 */
-	std::string cached_sexp() const {
-		return document().cached_sexp();
-	}
-
 	/*
 	 * Convert to Sexp
 	 */
 
 	/**
-	 * Get the s-expression for this message. Stays valid as long
-	 * as this message is.
+	 * Get the s-expression for this message. Stays valid as long as this
+	 * message is.
 	 *
-	 * @return a Mu::Sexp::List representing the message.
+	 * @return an Sexp representing the message.
 	 */
-	const Mu::Sexp::List& to_sexp_list() const;
-	Mu::Sexp to_sexp() const {
-		return Sexp::make_list(Sexp::List(to_sexp_list()));
-	}
-
-	/**
-	 * Update the cached sexp for this message which is stored in the
-	 * document. This should be done immediately before storing it in the
-	 * database.
-	 *
-	 */
-	void update_cached_sexp();
+	const Sexp& sexp() const;
 
 	/*
 	 * And some non-const message, for updating an existing
@@ -477,5 +459,15 @@ private:
 }; // Message
 MU_ENABLE_BITOPS(Message::Options);
 
+
+
+static inline std::ostream&
+operator<<(std::ostream& os, const Message& msg)
+{
+	os << msg.sexp();
+	return os;
+}
+
+
 } // Mu
 #endif /* MU_MESSAGE_HH__ */
diff --git a/lib/message/test-mu-message.cc b/lib/message/test-mu-message.cc
index a96b44bf..9cfc1a4d 100644
--- a/lib/message/test-mu-message.cc
+++ b/lib/message/test-mu-message.cc
@@ -481,8 +481,7 @@ Content-Type: message/rfc822
 )";
 	auto message{Message::make_from_text(msgtext)};
 	g_assert_true(!!message);
-
-	g_assert_true(message->cached_sexp().empty());
+	//g_assert_true(message->sexp().empty());
 }