Added hint about POP3 limitations

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

@@ -13,6 +13,16 @@
         android:layout_width="match_parent"
         android:layout_height="wrap_content">
 
+        <TextView
+            android:id="@+id/tvPopSupport"
+            android:layout_width="wrap_content"
+            android:layout_height="wrap_content"
+            android:text="@string/title_pop_support"
+            android:textAppearance="@style/TextAppearance.AppCompat.Small"
+            android:textStyle="italic|bold"
+            app:layout_constraintStart_toStartOf="parent"
+            app:layout_constraintTop_toTopOf="parent" />
+
         <TextView
             android:id="@+id/tvHost"
             android:layout_width="wrap_content"
@@ -21,7 +31,7 @@
             android:text="@string/title_host"
             android:textAppearance="@style/TextAppearance.AppCompat.Small"
             app:layout_constraintStart_toStartOf="parent"
-            app:layout_constraintTop_toTopOf="parent" />
+            app:layout_constraintTop_toBottomOf="@id/tvPopSupport" />
 
         <EditText
             android:id="@+id/etHost"

app/src/main/res/values/strings.xml

@@ -415,6 +415,7 @@
     <string name="title_identity_delete">Delete this identity permanently?</string>
     <string name="title_edit_html">Edit as HTML</string>
     <string name="title_last_connected">Last connected: %1$s</string>
+    <string name="title_pop_support">The POP3 protocol supports downloading and deleting messages only. So, it will not be possible to mark message favorite, move messages, etc. POP3 will use more battery power than IMAP. Therefore, consider using the IMAP protocol whenever possible.</string>
     <string name="title_activesync_support">ActiveSync is not supported</string>
     <string name="title_oauth_support">OAuth is not supported</string>
     <string name="title_authorize">Authorize</string>