Added leave delete hint

FAQ.md

@@ -2738,12 +2738,21 @@ that non-standard protocols, like Microsoft Exchange Web Services and Microsoft
 <a name="faq134"></a>
 **(134) Can you add deleting local messages?**
 
-Since locally deleted messages would be downloaded again on the next sync it is not possible to permanently delete local messages.
+*POP3*
 
-As an alternative you can hide messages,
+In the account settings (Setup, step 1, Manage, tap account) you can enable *Leave deleted messages on server*.
+
+*IMAP*
+
+Since the IMAP protocol is meant to synchronize two ways,
+deleting a message from the device would result in fetching the message again when synchronizing again.
+
+However, FairEmail supports hiding messages,
 either via the three-dots menu in the action bar just above the message text
 or by multiple selecting messages in the message list.
 
+It is also possible to set the swipe left or right action to hide a message.
+
 <br />
 
 <a name="faq135"></a>

app/src/main/java/eu/faircode/email/FragmentAccount.java

@@ -108,6 +108,7 @@ public class FragmentAccount extends FragmentBase {
     private Button btnAdvanced;
     private CheckBox cbSynchronize;
     private CheckBox cbOnDemand;
+    private TextView tvLeave;
     private CheckBox cbPrimary;
     private CheckBox cbNotify;
     private TextView tvNotifyPro;
@@ -221,6 +222,7 @@ public class FragmentAccount extends FragmentBase {
         btnAdvanced = view.findViewById(R.id.btnAdvanced);
         cbSynchronize = view.findViewById(R.id.cbSynchronize);
         cbOnDemand = view.findViewById(R.id.cbOnDemand);
+        tvLeave = view.findViewById(R.id.tvLeave);
         cbPrimary = view.findViewById(R.id.cbPrimary);
         cbNotify = view.findViewById(R.id.cbNotify);
         tvNotifyPro = view.findViewById(R.id.tvNotifyPro);
@@ -430,6 +432,14 @@ public class FragmentAccount extends FragmentBase {
             }
         });
 
+        tvLeave.getPaint().setUnderlineText(true);
+        tvLeave.setOnClickListener(new View.OnClickListener() {
+            @Override
+            public void onClick(View view) {
+                Helper.viewFAQ(getContext(), 134);
+            }
+        });
+
         if (Build.VERSION.SDK_INT < Build.VERSION_CODES.O) {
             Helper.hide(cbNotify);
             Helper.hide(view.findViewById(R.id.tvNotifyPro));

app/src/main/res/layout/fragment_account.xml

@@ -434,6 +434,17 @@
             app:layout_constraintStart_toStartOf="parent"
             app:layout_constraintTop_toBottomOf="@id/cbSynchronize" />
 
+        <eu.faircode.email.FixedTextView
+            android:id="@+id/tvLeave"
+            android:layout_width="wrap_content"
+            android:layout_height="wrap_content"
+            android:layout_marginTop="12dp"
+            android:text="@string/title_leave_deleted"
+            android:textAppearance="@style/TextAppearance.AppCompat.Small"
+            android:textColor="?android:attr/textColorLink"
+            app:layout_constraintStart_toStartOf="parent"
+            app:layout_constraintTop_toBottomOf="@id/cbOnDemand" />
+
         <CheckBox
             android:id="@+id/cbPrimary"
             android:layout_width="wrap_content"
@@ -441,7 +452,7 @@
             android:layout_marginTop="12dp"
             android:text="@string/title_primary_account"
             app:layout_constraintStart_toStartOf="parent"
-            app:layout_constraintTop_toBottomOf="@id/cbOnDemand" />
+            app:layout_constraintTop_toBottomOf="@id/tvLeave" />
 
         <CheckBox
             android:id="@+id/cbNotify"
@@ -941,7 +952,7 @@
             android:layout_height="0dp"
             app:constraint_referenced_ids="
                 cbNotify,tvNotifyPro,
-                cbSynchronize,cbOnDemand,cbPrimary,
+                cbSynchronize,cbOnDemand,tvLeave,cbPrimary,
                 cbBrowse,tvBrowseHint,
                 cbAutoSeen,
                 tvInterval,etInterval,tvIntervalRemark,