Here is my custom Type Converter.

public class StringListTypeConverter : TypeConverter<String, IEnumerable<String>>
{
    protected override IEnumerable<string> ConvertCore(String source)
    {
        if (source == null)
            yield break;

        foreach (var item in source.Split(','))
            yield return item.Trim();
    }
}

public class Source
{
    public String Some {get;set;}
}


public class Dest
{
    public IEnumerable<String> Some {get;set;}
}

// ... configuration
Mapper.CreateMap<String, IEnumerable<String>>().ConvertUsing<StringListTypeConverter>();
Mapper.CreateMap<Source, Dest>();

The problem: StringListTypeConverter is not being called at all. Dest.Some == null.