What's the best way to get Woyano whitelisted?

Our stats show that users are inviting other users onto the system, but it seems that EMail providers such as Yahoo, Gmail, Etc. Are putting us in the Spam folder :(

Does anyone know the best way to deal with this issue?

So far I have found two commercial services who deal with this:

• http://www.senderscorecertified.com/commercial.html
• http://www.habeas.com/en-US/Senders/Overview/

It seems like the whole email issue is riddled with problems.

In the mean time we have taken the usual steps of ensuring we have a valis spf record etc.