diff --git a/api/send-message.go b/api/send-message.go
index bd35c22..abc2700 100644
--- a/api/send-message.go
+++ b/api/send-message.go
@@ -3,6 +3,7 @@ package api
 import (
 	"encoding/json"
 	"errors"
+	"fmt"
 	postfixLookup "github.com/1f349/lotus/postfix-lookup"
 	"github.com/1f349/lotus/smtp"
 	"github.com/julienschmidt/httprouter"
@@ -34,12 +35,11 @@ func MessageSender(send Smtp) func(rw http.ResponseWriter, req *http.Request, pa
 		// prepare the mail for sending
 		mail, err := j.PrepareMail(timeNow())
 		if err != nil {
-			apiError(rw, http.StatusBadRequest, "Invalid mail message")
+			apiError(rw, http.StatusBadRequest, fmt.Sprintf("Invalid mail message: %s", err))
 			return
 		}
 
 		// this looks up the underlying account for the sender alias
-		println(mail.From)
 		lookup, err := defaultPostfixLookup(mail.From)
 
 		// the alias does not exist
diff --git a/api/send-message_test.go b/api/send-message_test.go
index 6829251..670c058 100644
--- a/api/send-message_test.go
+++ b/api/send-message_test.go
@@ -144,7 +144,67 @@ var messageSenderTestData = []struct {
 		smtp:   &fakeSmtp{},
 		claims: makeFakeAuthClaims("admin@example.com"),
 		status: http.StatusBadRequest,
-		output: "Invalid mail message",
+		output: "Invalid mail message: multiple from addresses",
+	},
+	{
+		req: func() (*http.Request, error) {
+			j, err := json.Marshal(smtp.Json{
+				From:     "noreply@example.com",
+				ReplyTo:  "admin@example.com",
+				To:       "user@example.com",
+				Subject:  "Test Subject",
+				BodyType: "no",
+				Body:     "Plain text",
+			})
+			if err != nil {
+				return nil, err
+			}
+			return http.NewRequest(http.MethodPost, "https://api.example.com/v1/mail/message", bytes.NewReader(j))
+		},
+		smtp:   &fakeSmtp{},
+		claims: makeFakeAuthClaims("admin@example.com"),
+		status: http.StatusBadRequest,
+		output: "Invalid mail message: invalid body type",
+	},
+	{
+		req: func() (*http.Request, error) {
+			j, err := json.Marshal(smtp.Json{
+				From:     "noreply@example.com",
+				ReplyTo:  "admin@example.com",
+				To:       "a <user@example.com",
+				Subject:  "Test Subject",
+				BodyType: "no",
+				Body:     "Plain text",
+			})
+			if err != nil {
+				return nil, err
+			}
+			return http.NewRequest(http.MethodPost, "https://api.example.com/v1/mail/message", bytes.NewReader(j))
+		},
+		smtp:   &fakeSmtp{},
+		claims: makeFakeAuthClaims("admin@example.com"),
+		status: http.StatusBadRequest,
+		output: "Invalid mail message: mail: unclosed angle-addr",
+	},
+	{
+		req: func() (*http.Request, error) {
+			j, err := json.Marshal(smtp.Json{
+				From:     "noreply@example.com",
+				ReplyTo:  "admin@example.com",
+				To:       "a <user>",
+				Subject:  "Test Subject",
+				BodyType: "no",
+				Body:     "Plain text",
+			})
+			if err != nil {
+				return nil, err
+			}
+			return http.NewRequest(http.MethodPost, "https://api.example.com/v1/mail/message", bytes.NewReader(j))
+		},
+		smtp:   &fakeSmtp{},
+		claims: makeFakeAuthClaims("admin@example.com"),
+		status: http.StatusBadRequest,
+		output: "Invalid mail message: mail: missing @ in addr-spec",
 	},
 	{
 		req: func() (*http.Request, error) {