Well, that was not what I expected.

gistfile1.cs

public class Source { public string Property { get; set; } }
public class Dest { public string Property { get; private set; } }

[Fact]
public void Wat()
{
    Mapper.CreateMap<Source, Dest>();
    var source = new Source {Property = "foo"};
    var dest = Mapper.Map<Dest>(source);
    
    Console.Out.Write(dest.Property); // "foo"
}