diff --git a/.travis.yml b/.travis.yml
index c179abd..d017f16 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -7,4 +7,5 @@ go:
 before_install:
   - go get -v github.com/google/go-querystring/query
   - go get -v github.com/h2non/gock
+  - go get -v github.com/stretchr/testify/assert
 script: go test -v ./...
diff --git a/v1/client_test.go b/v1/client_test.go
index 7f102d1..0cfc4b5 100644
--- a/v1/client_test.go
+++ b/v1/client_test.go
@@ -187,8 +187,8 @@ func TestMgClient_TextMessages(t *testing.T) {
 			Type:       MsgTypeText,
 			Text:       "hello!",
 		},
-		Originator: "user",
-		User: User{
+		Originator: OriginatorCustomer,
+		Customer: Customer{
 			ExternalID: "6",
 			Nickname:   "octopus",
 			Firstname:  "Joe",
@@ -228,8 +228,8 @@ func TestMgClient_ImageMessages(t *testing.T) {
 			Type:       MsgTypeImage,
 			Items:      []Item{{ID: uploadFileResponse.ID}},
 		},
-		Originator: "user",
-		User: User{
+		Originator: OriginatorCustomer,
+		Customer: Customer{
 			ExternalID: "6",
 			Nickname:   "octopus",
 			Firstname:  "Joe",
diff --git a/v1/types.go b/v1/types.go
index 43cfb56..646a463 100644
--- a/v1/types.go
+++ b/v1/types.go
@@ -1,6 +1,7 @@
 package v1
 
 import (
+	"errors"
 	"net/http"
 	"time"
 )
@@ -47,6 +48,13 @@ const (
 	FileSizeLimit = 20 * 1024 * 1024
 )
 
+const (
+	// OriginatorCustomer means message was created by customer
+	OriginatorCustomer Originator = iota + 1
+	// OriginatorChannel means message was created by channel, for example via messenger mobile application
+	OriginatorChannel
+)
+
 // MgClient type
 type MgClient struct {
 	URL        string       `json:"url"`
@@ -189,8 +197,8 @@ type Channels struct {
 	Limit       int       `url:"limit,omitempty" json:"limit,omitempty"`
 }
 
-// User struct
-type User struct {
+// Customer struct
+type Customer struct {
 	ExternalID string `json:"external_id"`
 	Nickname   string `json:"nickname"`
 	Firstname  string `json:"first_name,omitempty"`
@@ -233,8 +241,8 @@ type EditMessageRequestMessage struct {
 // SendData struct
 type SendData struct {
 	Message        Message                  `json:"message"`
-	Originator     string                   `json:"originator,omitempty"`
-	User           User                     `json:"user"`
+	Originator     Originator               `json:"originator,omitempty"`
+	Customer       Customer                 `json:"customer"`
 	Channel        uint64                   `json:"channel"`
 	ExternalChatID string                   `json:"external_chat_id"`
 	Quote          *SendMessageRequestQuote `json:"quote,omitempty"`
@@ -399,3 +407,20 @@ type TransportRequestMeta struct {
 	ID        uint64 `json:"id"`
 	Timestamp int64  `json:"timestamp"`
 }
+
+var ErrInvalidOriginator = errors.New("invalid originator")
+
+// Originator of message
+type Originator byte
+
+// MarshalText marshals originator to text
+func (o Originator) MarshalText() ([]byte, error) {
+	switch o {
+	case OriginatorCustomer:
+		return []byte("customer"), nil
+	case OriginatorChannel:
+		return []byte("channel"), nil
+	}
+
+	return nil, ErrInvalidOriginator
+}
diff --git a/v1/types_test.go b/v1/types_test.go
new file mode 100644
index 0000000..bb205fe
--- /dev/null
+++ b/v1/types_test.go
@@ -0,0 +1,104 @@
+package v1
+
+import (
+	"encoding/json"
+	"fmt"
+	"github.com/stretchr/testify/assert"
+	"testing"
+)
+
+func TestSendData_MarshalJSON(t *testing.T) {
+	t.Run("WithoutOriginator", func(t *testing.T) {
+		data, err := json.Marshal(SendData{})
+
+		assert.NoError(t, err)
+
+		expected := `{
+			"channel": 0,
+			"customer": {
+				"external_id": "",
+				"nickname": ""
+			},
+			"external_chat_id": "",
+			"message": {
+				"external_id": ""
+			}
+		}`
+		assert.JSONEq(t, expected, string(data))
+	})
+
+	t.Run("WithOriginator", func(t *testing.T) {
+		cases := []struct {
+			originator Originator
+			string     string
+		}{
+			{
+				OriginatorCustomer,
+				"customer",
+			},
+			{
+				OriginatorChannel,
+				"channel",
+			},
+		}
+
+		pattern := `{
+			"originator": "%s",
+			"channel": 0,
+			"customer": {
+				"external_id": "",
+				"nickname": ""
+			},
+			"external_chat_id": "",
+			"message": {
+				"external_id": ""
+			}
+		}`
+
+		for _, c := range cases {
+			data, err := json.Marshal(SendData{
+				Originator: c.originator,
+			})
+
+			assert.NoError(t, err)
+			assert.JSONEq(t, fmt.Sprintf(pattern, c.string), string(data))
+		}
+	})
+}
+
+func TestOriginator(t *testing.T) {
+	b, err := OriginatorCustomer.MarshalText()
+	assert.NoError(t, err)
+	assert.Equal(t, "customer", string(b))
+
+	b, err = OriginatorChannel.MarshalText()
+	assert.NoError(t, err)
+	assert.Equal(t, "channel", string(b))
+
+	t.Run("MarshalText_Valid", func(t *testing.T) {
+		cases := []struct {
+			byte     byte
+			expected string
+		}{
+			{1, "customer"},
+			{2, "channel"},
+		}
+		for _, c := range cases {
+			result, err := Originator(c.byte).MarshalText()
+			assert.NoError(t, err)
+			assert.Equal(t, c.expected, string(result))
+		}
+	})
+
+	t.Run("MarshalText_Invalid", func(t *testing.T) {
+		data, err := Originator(0).MarshalText()
+		assert.Nil(t, data)
+		assert.Equal(t, err, ErrInvalidOriginator)
+	})
+
+	t.Run("MarshalJSON_Invalid", func(t *testing.T) {
+		data, err := json.Marshal(Originator(3))
+		assert.Nil(t, data)
+		assert.EqualError(t, err, "json: error calling MarshalJSON for type v1.Originator: invalid originator")
+	})
+}