diff --git a/app/src/main/java/i2p/bote/android/NewEmailFragment.java b/app/src/main/java/i2p/bote/android/NewEmailFragment.java
index f9d8d82..55b80dd 100644
--- a/app/src/main/java/i2p/bote/android/NewEmailFragment.java
+++ b/app/src/main/java/i2p/bote/android/NewEmailFragment.java
@@ -98,6 +98,8 @@ public class NewEmailFragment extends Fragment {
 
     public static final String QUOTE_MSG_TYPE = "type";
 
+    private static final long MAX_RECOMMENDED_ATTACHMENT_SIZE = 1048576;
+
     private static final int REQUEST_FILE = 1;
 
     private String mSenderKey;
@@ -112,6 +114,8 @@ public class NewEmailFragment extends Fragment {
     EditText mSubject;
     EditText mContent;
     LinearLayout mAttachments;
+    private long mTotalAttachmentSize;
+    private View mAttachmentSizeWarning;
     boolean mMoreVisible;
     boolean mDirty;
 
@@ -455,17 +459,45 @@ public class NewEmailFragment extends Fragment {
             v.findViewById(R.id.attachment_action).setOnClickListener(new View.OnClickListener() {
                 @Override
                 public void onClick(View view) {
+                    updateAttachmentSizeCount(attachment.getSize(), false);
                     attachment.clean();
                     mAttachments.removeView(v);
                 }
             });
             mAttachments.addView(v);
+            updateAttachmentSizeCount(attachment.getSize(), true);
         } catch (FileNotFoundException e) {
             e.printStackTrace();
             Log.e(Constants.ANDROID_LOG_TAG, "File not found: " + uri);
         }
     }
 
+    private void updateAttachmentSizeCount(long size, boolean increase) {
+        if (increase) {
+            mTotalAttachmentSize += size;
+            if (mTotalAttachmentSize > MAX_RECOMMENDED_ATTACHMENT_SIZE &&
+                    mAttachmentSizeWarning == null) {
+                mAttachmentSizeWarning = getActivity().getLayoutInflater().inflate(
+                        R.layout.listitem_attachment_warning, mAttachments, false);
+                TextView warning = (TextView) mAttachmentSizeWarning.findViewById(
+                        R.id.attachment_warning_text);
+                warning.setText(
+                        getString(R.string.attachment_size_warning,
+                                BoteHelper.getHumanReadableSize(
+                                        getActivity(), MAX_RECOMMENDED_ATTACHMENT_SIZE))
+                );
+                mAttachments.addView(mAttachmentSizeWarning, 0);
+            }
+        } else {
+            mTotalAttachmentSize -= size;
+            if (mTotalAttachmentSize <= MAX_RECOMMENDED_ATTACHMENT_SIZE &&
+                    mAttachmentSizeWarning != null) {
+                mAttachments.removeView(mAttachmentSizeWarning);
+                mAttachmentSizeWarning = null;
+            }
+        }
+    }
+
     private boolean sendEmail() {
         Email email = new Email(I2PBote.getInstance().getConfiguration().getIncludeSentTime());
         try {
diff --git a/app/src/main/java/i2p/bote/android/util/BoteHelper.java b/app/src/main/java/i2p/bote/android/util/BoteHelper.java
index e08b920..fd99ffd 100644
--- a/app/src/main/java/i2p/bote/android/util/BoteHelper.java
+++ b/app/src/main/java/i2p/bote/android/util/BoteHelper.java
@@ -28,9 +28,11 @@ import java.io.IOException;
 import java.io.InputStream;
 import java.io.OutputStream;
 import java.security.GeneralSecurityException;
+import java.text.NumberFormat;
 import java.util.Collection;
 import java.util.Iterator;
 import java.util.List;
+import java.util.Locale;
 
 import javax.mail.Address;
 import javax.mail.MessagingException;
@@ -503,4 +505,21 @@ public class BoteHelper extends GeneralHelper {
             Log.e(Constants.ANDROID_LOG_TAG, "Exception copying streams", e);
         }
     }
+
+    public static String getHumanReadableSize(Context context, long size) {
+        int unit = (63-Long.numberOfLeadingZeros(size)) / 10;   // 0 if totalBytes<1K, 1 if 1K<=totalBytes<1M, etc.
+        double value = (double)size / (1<<(10*unit));
+        int formatStr;
+        switch (unit) {
+            case 0: formatStr = R.string.n_bytes; break;
+            case 1: formatStr = R.string.n_kilobytes; break;
+            default: formatStr = R.string.n_megabytes;
+        }
+        NumberFormat formatter = NumberFormat.getInstance(Locale.getDefault());
+        if (value < 100)
+            formatter.setMaximumFractionDigits(1);
+        else
+            formatter.setMaximumFractionDigits(0);
+        return context.getString(formatStr, formatter.format(value));
+    }
 }
diff --git a/app/src/main/java/i2p/bote/android/util/ContentAttachment.java b/app/src/main/java/i2p/bote/android/util/ContentAttachment.java
index 0fceaf9..8ef2435 100644
--- a/app/src/main/java/i2p/bote/android/util/ContentAttachment.java
+++ b/app/src/main/java/i2p/bote/android/util/ContentAttachment.java
@@ -10,8 +10,6 @@ import java.io.FileNotFoundException;
 import java.io.IOException;
 import java.io.InputStream;
 import java.io.OutputStream;
-import java.text.NumberFormat;
-import java.util.Locale;
 
 import javax.activation.DataHandler;
 import javax.activation.DataSource;
@@ -19,7 +17,6 @@ import javax.mail.MessagingException;
 import javax.mail.Part;
 
 import i2p.bote.Util;
-import i2p.bote.android.R;
 import i2p.bote.email.Attachment;
 
 public class ContentAttachment implements Attachment {
@@ -89,20 +86,7 @@ public class ContentAttachment implements Attachment {
     }
 
     public String getHumanReadableSize() {
-        int unit = (63-Long.numberOfLeadingZeros(mSize)) / 10;   // 0 if totalBytes<1K, 1 if 1K<=totalBytes<1M, etc.
-        double value = (double)mSize / (1<<(10*unit));
-        int formatStr;
-        switch (unit) {
-            case 0: formatStr = R.string.n_bytes; break;
-            case 1: formatStr = R.string.n_kilobytes; break;
-            default: formatStr = R.string.n_megabytes;
-        }
-        NumberFormat formatter = NumberFormat.getInstance(Locale.getDefault());
-        if (value < 100)
-            formatter.setMaximumFractionDigits(1);
-        else
-            formatter.setMaximumFractionDigits(0);
-        return mCtx.getString(formatStr, formatter.format(value));
+        return BoteHelper.getHumanReadableSize(mCtx, mSize);
     }
 
     @Override
diff --git a/app/src/main/res/values/strings.xml b/app/src/main/res/values/strings.xml
index 3cc3ce4..57cd272 100644
--- a/app/src/main/res/values/strings.xml
+++ b/app/src/main/res/values/strings.xml
@@ -127,6 +127,8 @@
     <string name="compose">Compose</string>
     <string name="subject">Subject</string>
     <string name="compose_email">Compose email</string>
+    <!-- Argument is a file size, e.g. "500 KB" -->
+    <string name="attachment_size_warning">You have more than %s of attachments. Email sending may be slow.</string>
     <string name="add_one_recipient">Add at least one recipient.</string>
     <string name="stop_composing_email">Stop composing email?</string>
     <string name="all_changes_will_be_discarded">All changes will be discarded.</string>