They said in the PWS workshop that it's just difficult since every individual provider has different settings. Add to that any customizing the recipient does, and you've got an unlimited number of obstacles to overcome.
Constant Contact and iContact have agreements with most ISPs (internet service providers) to allow their messages through. HO doesn't have the resources to undertake the huge task of establishing those agreements. It's not their primary business, so the return would be miniscule.But why is it that constant contact and icontact seem to have a higher percentage rate of getting through to different email servers. Until I can see who is opening my emails I will never send out an email through PWS to my customers.