diff --git a/internal/imap/store.go b/internal/imap/store.go
index 005108c3..137c916c 100644
--- a/internal/imap/store.go
+++ b/internal/imap/store.go
@@ -31,7 +31,7 @@ import (
 type storeUserProvider interface {
 	UserID() string
 	GetSpace() (usedSpace, maxSpace uint, err error)
-	GetMaxUpload() (uint, error)
+	GetMaxUpload() (int64, error)
 
 	GetAddress(addressID string) (storeAddressProvider, error)
 
diff --git a/internal/smtp/store.go b/internal/smtp/store.go
index 4f0218a6..42a1bbd0 100644
--- a/internal/smtp/store.go
+++ b/internal/smtp/store.go
@@ -33,4 +33,5 @@ type storeUserProvider interface {
 		attachedPublicKeyName string,
 		parentID string) (*pmapi.Message, []*pmapi.Attachment, error)
 	SendMessage(messageID string, req *pmapi.SendMessageReq) error
+	GetMaxUpload() (int64, error)
 }
diff --git a/internal/smtp/user.go b/internal/smtp/user.go
index 202c3166..62d31407 100644
--- a/internal/smtp/user.go
+++ b/internal/smtp/user.go
@@ -20,9 +20,11 @@
 package smtp
 
 import (
+	"bytes"
 	"encoding/base64"
 	"fmt"
 	"io"
+	"io/ioutil"
 	"mime"
 	"net/mail"
 	"strings"
@@ -319,6 +321,12 @@ func (su *smtpUser) Send(returnPath string, to []string, messageReader io.Reader
 		return nil
 	}
 
+	if ok, err := su.isTotalSizeOkay(message, attReaders); err != nil {
+		return err
+	} else if !ok {
+		return errors.New("message is too large")
+	}
+
 	su.backend.sendRecorder.addMessage(sendRecorderMessageHash)
 	message, atts, err := su.storeUser.CreateDraft(kr, message, attReaders, attachedPublicKey, attachedPublicKeyName, parentID)
 	if err != nil {
@@ -527,3 +535,24 @@ func (su *smtpUser) Logout() error {
 	log.Debug("SMTP client logged out user ", su.addressID)
 	return nil
 }
+
+func (su *smtpUser) isTotalSizeOkay(message *pmapi.Message, attReaders []io.Reader) (bool, error) {
+	maxUpload, err := su.storeUser.GetMaxUpload()
+	if err != nil {
+		return false, err
+	}
+
+	var attSize int64
+
+	for i := range attReaders {
+		b, err := ioutil.ReadAll(attReaders[i])
+		if err != nil {
+			return false, err
+		}
+
+		attSize += int64(len(b))
+		attReaders[i] = bytes.NewBuffer(b)
+	}
+
+	return message.Size+attSize <= maxUpload, nil
+}
diff --git a/internal/store/user.go b/internal/store/user.go
index b0b92150..d234776b 100644
--- a/internal/store/user.go
+++ b/internal/store/user.go
@@ -31,11 +31,11 @@ func (store *Store) GetSpace() (usedSpace, maxSpace uint, err error) {
 	return uint(apiUser.UsedSpace), uint(apiUser.MaxSpace), nil
 }
 
-// GetMaxUpload returns max size of attachment in bytes.
-func (store *Store) GetMaxUpload() (uint, error) {
+// GetMaxUpload returns max size of message + all attachments in bytes.
+func (store *Store) GetMaxUpload() (int64, error) {
 	apiUser, err := store.client().CurrentUser()
 	if err != nil {
 		return 0, err
 	}
-	return uint(apiUser.MaxUpload), nil
+	return apiUser.MaxUpload, nil
 }
diff --git a/test/accounts/fake.json b/test/accounts/fake.json
index 60bea18a..79ba3742 100644
--- a/test/accounts/fake.json
+++ b/test/accounts/fake.json
@@ -2,23 +2,28 @@
     "users": {
         "user": {
             "ID": "1",
-            "Name": "user"
+            "Name": "user",
+            "MaxUpload": 26214400
         },
         "user2fa": {
             "ID": "2",
-            "Name": "user2fa"
+            "Name": "user2fa",
+            "MaxUpload": 26214400
         },
         "userAddressWithCapitalLetter": {
             "ID": "3",
-            "Name": "userAddressWithCapitalLetter"
+            "Name": "userAddressWithCapitalLetter",
+            "MaxUpload": 26214400
         },
         "userMoreAddresses": {
             "ID": "4",
-            "Name": "userMoreAddresses"
+            "Name": "userMoreAddresses",
+            "MaxUpload": 26214400
         },
         "userDisabledPrimaryAddress": {
             "ID": "5",
-            "Name": "userDisabledPrimaryAddress"
+            "Name": "userDisabledPrimaryAddress",
+            "MaxUpload": 26214400
         }
     },
     "addresses": {
diff --git a/unreleased.md b/unreleased.md
index eb902ee8..08229b87 100644
--- a/unreleased.md
+++ b/unreleased.md
@@ -5,6 +5,7 @@ Changelog [format](http://keepachangelog.com/en/1.0.0/)
 ## Unreleased
 
 ### Added
+* GODT-928 Reject messages which are too large.
 
 ### Removed
 * Remove dependency on go-apple-mobileconfig.