diff --git a/autotests/private/protocoltest.cpp b/autotests/private/protocoltest.cpp
--- a/autotests/private/protocoltest.cpp
+++ b/autotests/private/protocoltest.cpp
@@ -39,7 +39,7 @@
     // If it wasn't you who broke it, please go find that person who was too
     // lazy to extend the test case and beat them with a stick. -- Dan
 
-    QCOMPARE(Akonadi::Protocol::version(), 52);
+    QCOMPARE(Akonadi::Protocol::version(), 53);
 }
 
 void ProtocolTest::testFactory_data()
diff --git a/autotests/server/relationhandlertest.cpp b/autotests/server/relationhandlertest.cpp
--- a/autotests/server/relationhandlertest.cpp
+++ b/autotests/server/relationhandlertest.cpp
@@ -325,33 +325,33 @@
             TestScenario::List scenarios;
             scenarios << FakeAkonadiServer::loginScenario()
                       << TestScenario::create(5, TestScenario::ClientCmd, Protocol::FetchRelationsCommand(-1, { "type" }))
-                      << TestScenario::create(5, TestScenario::ServerCmd, Protocol::FetchRelationsResponse(item1.id(), item2.id(), { "type" }, "foobar1"))
-                      << TestScenario::create(5, TestScenario::ServerCmd, Protocol::FetchRelationsResponse(item3.id(), item4.id(), { "type" }, "foobar3"))
-                      << TestScenario::create(5, TestScenario::ServerCmd, Protocol::FetchRelationsResponse(item4.id(), item3.id(), { "type" }, "foobar4"))
+                      << TestScenario::create(5, TestScenario::ServerCmd, Protocol::FetchRelationsResponse(item1.id(), item1.mimeType().name().toUtf8(), item2.id(), item2.mimeType().name().toUtf8(), { "type" }, "foobar1"))
+                      << TestScenario::create(5, TestScenario::ServerCmd, Protocol::FetchRelationsResponse(item3.id(), item3.mimeType().name().toUtf8(), item4.id(), item4.mimeType().name().toUtf8(), { "type" }, "foobar3"))
+                      << TestScenario::create(5, TestScenario::ServerCmd, Protocol::FetchRelationsResponse(item4.id(), item4.mimeType().name().toUtf8(), item3.id(), item3.mimeType().name().toUtf8(), { "type" }, "foobar4"))
                       << TestScenario::create(5, TestScenario::ServerCmd, Protocol::FetchRelationsResponse());
 
             QTest::newRow("filter by type") << scenarios;
         }
         {
             TestScenario::List scenarios;
             scenarios << FakeAkonadiServer::loginScenario()
                       << TestScenario::create(5, TestScenario::ClientCmd, Protocol::FetchRelationsCommand())
-                      << TestScenario::create(5, TestScenario::ServerCmd, Protocol::FetchRelationsResponse(item1.id(), item2.id(), { "type" }, "foobar1"))
-                      << TestScenario::create(5, TestScenario::ServerCmd, Protocol::FetchRelationsResponse(item1.id(), item2.id(), { "type2" }, "foobar2"))
-                      << TestScenario::create(5, TestScenario::ServerCmd, Protocol::FetchRelationsResponse(item3.id(), item4.id(), { "type" }, "foobar3"))
-                      << TestScenario::create(5, TestScenario::ServerCmd, Protocol::FetchRelationsResponse(item4.id(), item3.id(), { "type" }, "foobar4"))
+                      << TestScenario::create(5, TestScenario::ServerCmd, Protocol::FetchRelationsResponse(item1.id(), item1.mimeType().name().toUtf8(), item2.id(), item2.mimeType().name().toUtf8(), { "type" }, "foobar1"))
+                      << TestScenario::create(5, TestScenario::ServerCmd, Protocol::FetchRelationsResponse(item1.id(), item1.mimeType().name().toUtf8(), item2.id(), item2.mimeType().name().toUtf8(), { "type2" }, "foobar2"))
+                      << TestScenario::create(5, TestScenario::ServerCmd, Protocol::FetchRelationsResponse(item3.id(), item3.mimeType().name().toUtf8(), item4.id(), item4.mimeType().name().toUtf8(), { "type" }, "foobar3"))
+                      << TestScenario::create(5, TestScenario::ServerCmd, Protocol::FetchRelationsResponse(item4.id(), item4.mimeType().name().toUtf8(), item3.id(), item3.mimeType().name().toUtf8(), { "type" }, "foobar4"))
                       << TestScenario::create(5, TestScenario::ServerCmd, Protocol::FetchRelationsResponse());
 
             QTest::newRow("no filter") << scenarios;
         }
         {
             TestScenario::List scenarios;
             scenarios << FakeAkonadiServer::loginScenario()
                       << TestScenario::create(5, TestScenario::ClientCmd, Protocol::FetchRelationsCommand(-1, {}, QLatin1String("testresource")))
-                      << TestScenario::create(5, TestScenario::ServerCmd, Protocol::FetchRelationsResponse(item1.id(), item2.id(), { "type" }, "foobar1"))
-                      << TestScenario::create(5, TestScenario::ServerCmd, Protocol::FetchRelationsResponse(item1.id(), item2.id(), { "type2" }, "foobar2"))
-                      << TestScenario::create(5, TestScenario::ServerCmd, Protocol::FetchRelationsResponse(item3.id(), item4.id(), { "type" }, "foobar3"))
-                      << TestScenario::create(5, TestScenario::ServerCmd, Protocol::FetchRelationsResponse(item4.id(), item3.id(), { "type" }, "foobar4"))
+                      << TestScenario::create(5, TestScenario::ServerCmd, Protocol::FetchRelationsResponse(item1.id(), item1.mimeType().name().toUtf8(), item2.id(), item2.mimeType().name().toUtf8(), { "type" }, "foobar1"))
+                      << TestScenario::create(5, TestScenario::ServerCmd, Protocol::FetchRelationsResponse(item1.id(), item1.mimeType().name().toUtf8(), item2.id(), item2.mimeType().name().toUtf8(), { "type2" }, "foobar2"))
+                      << TestScenario::create(5, TestScenario::ServerCmd, Protocol::FetchRelationsResponse(item3.id(), item3.mimeType().name().toUtf8(), item4.id(), item4.mimeType().name().toUtf8(), { "type" }, "foobar3"))
+                      << TestScenario::create(5, TestScenario::ServerCmd, Protocol::FetchRelationsResponse(item4.id(), item4.mimeType().name().toUtf8(), item3.id(), item3.mimeType().name().toUtf8(), { "type" }, "foobar4"))
                       << TestScenario::create(5, TestScenario::ServerCmd, Protocol::FetchRelationsResponse());
 
             QTest::newRow("filter by resource with matching resource") << scenarios;
@@ -373,26 +373,26 @@
             TestScenario::List scenarios;
             scenarios << FakeAkonadiServer::loginScenario()
                       << TestScenario::create(5, TestScenario::ClientCmd, Protocol::FetchRelationsCommand(item1.id(), -1, { "type" }))
-                      << TestScenario::create(5, TestScenario::ServerCmd, Protocol::FetchRelationsResponse(item1.id(), item2.id(), "type", "foobar1"))
+                      << TestScenario::create(5, TestScenario::ServerCmd, Protocol::FetchRelationsResponse(item1.id(), item1.mimeType().name().toUtf8(), item2.id(), item2.mimeType().name().toUtf8(), "type", "foobar1"))
                       << TestScenario::create(5, TestScenario::ServerCmd, Protocol::FetchRelationsResponse());
 
             QTest::newRow("filter by left and type") << scenarios;
         }
         {
             TestScenario::List scenarios;
             scenarios << FakeAkonadiServer::loginScenario()
                       << TestScenario::create(5, TestScenario::ClientCmd, Protocol::FetchRelationsCommand(-1, item2.id(), { "type" }))
-                      << TestScenario::create(5, TestScenario::ServerCmd, Protocol::FetchRelationsResponse(item1.id(), item2.id(), "type", "foobar1"))
+                      << TestScenario::create(5, TestScenario::ServerCmd, Protocol::FetchRelationsResponse(item1.id(), item1.mimeType().name().toUtf8(), item2.id(), item2.mimeType().name().toUtf8(), "type", "foobar1"))
                       << TestScenario::create(5, TestScenario::ServerCmd, Protocol::FetchRelationsResponse());
 
             QTest::newRow("filter by right and type") << scenarios;
         }
         {
             TestScenario::List scenarios;
             scenarios << FakeAkonadiServer::loginScenario()
                       << TestScenario::create(5, TestScenario::ClientCmd, Protocol::FetchRelationsCommand(item3.id(), { "type" }))
-                      << TestScenario::create(5, TestScenario::ServerCmd, Protocol::FetchRelationsResponse(item3.id(), item4.id(), "type", "foobar3"))
-                      << TestScenario::create(5, TestScenario::ServerCmd, Protocol::FetchRelationsResponse(item4.id(), item3.id(), "type", "foobar4"))
+                      << TestScenario::create(5, TestScenario::ServerCmd, Protocol::FetchRelationsResponse(item3.id(), item3.mimeType().name().toUtf8(), item4.id(), item4.mimeType().name().toUtf8(), "type", "foobar3"))
+                      << TestScenario::create(5, TestScenario::ServerCmd, Protocol::FetchRelationsResponse(item4.id(), item4.mimeType().name().toUtf8(), item3.id(), item3.mimeType().name().toUtf8(), "type", "foobar4"))
                       << TestScenario::create(5, TestScenario::ServerCmd, Protocol::FetchRelationsResponse());
 
             QTest::newRow("fetch by side with typefilter") << scenarios;
diff --git a/src/private/protocol.cpp b/src/private/protocol.cpp
--- a/src/private/protocol.cpp
+++ b/src/private/protocol.cpp
@@ -49,7 +49,7 @@
 namespace Protocol {
 
 int version() {
-    return 52;
+    return 53;
 }
 
 }
@@ -2703,55 +2703,68 @@
 class FetchRelationsResponsePrivate : public ResponsePrivate
 {
 public:
-    FetchRelationsResponsePrivate(qint64 left = -1, qint64 right = -1,
+    FetchRelationsResponsePrivate(qint64 left = -1, const QByteArray &leftMimeType = QByteArray(),
+                                  qint64 right = -1, const QByteArray &rightMimeType = QByteArray(),
                                   const QByteArray &type = QByteArray(),
                                   const QByteArray &remoteId = QByteArray())
         : ResponsePrivate(Command::FetchRelations)
         , left(left)
+        , leftMimeType(leftMimeType)
         , right(right)
+        , rightMimeType(rightMimeType)
         , type(type)
         , remoteId(remoteId)
     {}
     FetchRelationsResponsePrivate(const FetchRelationsResponsePrivate &other)
         : ResponsePrivate(other)
         , left(other.left)
+        , leftMimeType(other.leftMimeType)
         , right(other.right)
+        , rightMimeType(other.rightMimeType)
         , type(other.type)
         , remoteId(other.remoteId)
     {}
 
     bool compare(const CommandPrivate* other) const Q_DECL_OVERRIDE
     {
         return ResponsePrivate::compare(other)
             && COMPARE(left)
+            && COMPARE(leftMimeType)
             && COMPARE(right)
+            && COMPARE(rightMimeType)
             && COMPARE(type)
             && COMPARE(remoteId);
     }
 
     DataStream &serialize(DataStream &stream) const Q_DECL_OVERRIDE
     {
         return ResponsePrivate::serialize(stream)
                << left
+               << leftMimeType
                << right
+               << rightMimeType
                << type
                << remoteId;
     }
 
     DataStream &deserialize(DataStream &stream) Q_DECL_OVERRIDE
     {
         return ResponsePrivate::deserialize(stream)
                >> left
+               >> leftMimeType
                >> right
+               >> rightMimeType
                >> type
                >> remoteId;
     }
 
     void debugString(DebugBlock &blck) const Q_DECL_OVERRIDE
     {
         ResponsePrivate::debugString(blck);
         blck.write("Left", left);
+        blck.write("LeftMimeType", leftMimeType);
         blck.write("Right", right);
+        blck.write("RightMimeType", rightMimeType);
         blck.write("Type", type);
         blck.write("Remote ID", remoteId);
     }
@@ -2762,7 +2775,9 @@
     }
 
     qint64 left;
+    QByteArray leftMimeType;
     qint64 right;
+    QByteArray rightMimeType;
     QByteArray type;
     QByteArray remoteId;
 };
@@ -2777,10 +2792,11 @@
 {
 }
 
-FetchRelationsResponse::FetchRelationsResponse(qint64 left, qint64 right,
+FetchRelationsResponse::FetchRelationsResponse(qint64 left, const QByteArray &leftMimeType,
+                                               qint64 right, const QByteArray &rightMimeType,
                                                const QByteArray &type,
                                                const QByteArray &remoteId)
-    : Response(new FetchRelationsResponsePrivate(left, right, type, remoteId))
+    : Response(new FetchRelationsResponsePrivate(left, leftMimeType, right, rightMimeType, type, remoteId))
 {
 }
 
@@ -2794,10 +2810,18 @@
 {
     return d_func()->left;
 }
+QByteArray FetchRelationsResponse::leftMimeType() const
+{
+    return d_func()->leftMimeType;
+}
 qint64 FetchRelationsResponse::right() const
 {
     return d_func()->right;
 }
+QByteArray FetchRelationsResponse::rightMimeType() const
+{
+    return d_func()->rightMimeType;
+}
 QByteArray FetchRelationsResponse::type() const
 {
     return d_func()->type;
diff --git a/src/private/protocol_p.h b/src/private/protocol_p.h
--- a/src/private/protocol_p.h
+++ b/src/private/protocol_p.h
@@ -774,12 +774,14 @@
 {
 public:
     explicit FetchRelationsResponse();
-    explicit FetchRelationsResponse(qint64 left, qint64 right, const QByteArray &type,
+    explicit FetchRelationsResponse(qint64 left, const QByteArray &leftMimeType, qint64 right, const QByteArray &rightMimeType, const QByteArray &type,
                                     const QByteArray &remoteId = QByteArray());
     FetchRelationsResponse(const Command &command);
 
     qint64 left() const;
+    QByteArray leftMimeType() const;
     qint64 right() const;
+    QByteArray rightMimeType() const;
     QByteArray type() const;
 
     void setRemoteId(const QByteArray &remoteId);
diff --git a/src/server/handler/relationfetch.cpp b/src/server/handler/relationfetch.cpp
--- a/src/server/handler/relationfetch.cpp
+++ b/src/server/handler/relationfetch.cpp
@@ -77,7 +77,8 @@
     }
     const Relation::List existingRelations = relationQuery.result();
     Q_FOREACH (const Relation &relation, existingRelations) {
-        sendResponse(Protocol::FetchRelationsResponse(relation.leftId(), relation.rightId(),
+        sendResponse(Protocol::FetchRelationsResponse(relation.leftId(), relation.left().mimeType().name().toUtf8(),
+                                                      relation.rightId(), relation.right().mimeType().name().toUtf8(),
                                                       relation.relationType().name().toUtf8(),
                                                       relation.remoteId().toUtf8()));
     }
diff --git a/src/server/handlerhelper.cpp b/src/server/handlerhelper.cpp
--- a/src/server/handlerhelper.cpp
+++ b/src/server/handlerhelper.cpp
@@ -239,7 +239,9 @@
 Protocol::FetchRelationsResponse HandlerHelper::fetchRelationsResponse(const Relation &relation)
 {
     return Protocol::FetchRelationsResponse(relation.leftId(),
+                                            relation.left().mimeType().name().toUtf8(),
                                             relation.rightId(),
+                                            relation.right().mimeType().name().toUtf8(),
                                             relation.relationType().name().toUtf8());
 }