What do you guys do with your returned mail postcards

[Cashmere Robinson]

Im looking to do another mailing campaign but so many of my postcards came back. Some marked vacant. Others simply not deliverable. Here's my question what do I do with the returned mail postcards should I just remove them off my list? If you use a skip trace are your results better if you possibly find a number connected with the property. Thanx in advance for the help