diff --git a/app/src/main/java/eu/faircode/email/FragmentCompose.java b/app/src/main/java/eu/faircode/email/FragmentCompose.java
index 140a7bebb6..62c4897873 100644
--- a/app/src/main/java/eu/faircode/email/FragmentCompose.java
+++ b/app/src/main/java/eu/faircode/email/FragmentCompose.java
@@ -326,6 +326,7 @@ public class FragmentCompose extends FragmentBase {
     private static final int COPY_ATTACHMENT_TIMEOUT = 60; // seconds
 
     private static final int MAX_QUOTE_LEVEL = 5;
+    private static final int MAX_REASONABLE_SIZE = 5 * 1024 * 1024;
 
     private static final int REQUEST_CONTACT_TO = 1;
     private static final int REQUEST_CONTACT_CC = 2;
@@ -6922,7 +6923,10 @@ public class FragmentCompose extends FragmentBase {
                         }
                     }
 
-                    Helper.writeText(draft.getFile(context), body);
+                    File f = draft.getFile(context);
+                    Helper.writeText(f, body);
+                    if (f.length() > MAX_REASONABLE_SIZE)
+                        args.putBoolean("large", true);
 
                     String full = HtmlHelper.getFullText(body);
                     draft.preview = HtmlHelper.getPreview(full);
@@ -7296,6 +7300,9 @@ public class FragmentCompose extends FragmentBase {
             bottom_navigation.getMenu().findItem(R.id.action_undo).setVisible(draft.revision > 1);
             bottom_navigation.getMenu().findItem(R.id.action_redo).setVisible(draft.revision < draft.revisions);
 
+            if (args.getBoolean("large"))
+                ToastEx.makeText(getContext(), R.string.title_large_body, Toast.LENGTH_LONG).show();
+
             if (args.getBundle("extras").getBoolean("silent")) {
                 etBody.setTag(null);
                 return;
diff --git a/app/src/main/res/values/strings.xml b/app/src/main/res/values/strings.xml
index e52708bc23..1d716e8675 100644
--- a/app/src/main/res/values/strings.xml
+++ b/app/src/main/res/values/strings.xml
@@ -2237,6 +2237,7 @@
     <string name="title_no_ask_again">Do not ask this again</string>
     <string name="title_no_ask_for_again">Do not ask this again for %1$s</string>
     <string name="title_no_body">No message text found</string>
+    <string name="title_large_body">This message is very large and this may cause problems!</string>
     <string name="title_no_charset">Unsupported encoding: %1$s</string>
     <string name="title_via">Via: %1$s</string>
     <string name="title_1hour">1 hour</string>