like so (and I meant "string", not "Address"); note that I haven't
implemented notifications against AddressLine1 etc; this could be
done, but you'd need to work with a subclass of Collection<string>, or
switch to BindingList<string> (which also works), and handle the
insert/etc.

Marc

using System;
using System.Collections.ObjectModel;
using System.Xml.Serialization;
using System.ComponentModel;
using System.Collections.Generic;

class Program
{
   static void Main(string[] args)
   {
       Sender s = new Sender();
       s.Name = "Test Name";
       s.AddressLine3 = "Test 3";
       s.AddressLine1 = "Test 1";
       XmlSerializer ser = new XmlSerializer(typeof(Sender));
       ser.Serialize(Console.Out, s);
   }
}

[Serializable]
public sealed class Sender : INotifyPropertyChanged
{
   [XmlIgnore]
   public string AddressLine1 {
       get { return GetAddressLine(0); }
       set { SetAddressLine(0,value); }
   }
   [XmlIgnore]
   public string AddressLine2
   {
       get { return GetAddressLine(1); }
       set { SetAddressLine(1,value); }
   }
   [XmlIgnore]
   public string AddressLine3
   {
       get { return GetAddressLine(2); }
       set { SetAddressLine(2,value); }
   }
   public string GetAddressLine(int index)
   {
       return AddressLines.Count > index ? AddressLines[index] : "";
   }
   public void SetAddressLine(int index, string value)
   {
       while (AddressLines.Count <= index)
       {
           AddressLines.Add("");
       }
       AddressLines[index] = value;
   }

   string name;
   public string Name { get { return name; } set {SetField(ref name,
value, "Name");}}

   readonly Collection<string> addressLines = new
Collection<string>();
   [XmlElement("Address")]
   public Collection<string> AddressLines {get {return
addressLines;}}

   public event PropertyChangedEventHandler PropertyChanged;

   private void SetField<T>(ref T field, T value, string
propertyName) {
       if(EqualityComparer<T>.Default.Equals(field,value)) return; //
no change
       field = value;
       PropertyChangedEventHandler handler = PropertyChanged;
       if (handler != null) {
           handler(this, new PropertyChangedEventArgs(propertyName));
       }
   }
}