The Surveymonkey survey tools allow you to configure a FROM address on survey invitations that get sent out by e-mail which - you guessed no prizes for guessing- in our case is set to survey@terena<email@example.com>.
Unfortunately the resulting e-mail is being sent with that very address as the envelop.
We publish SPF records with the "-all" flag (Allow domain's MXes to send mail for the domain, prohibit all others), so anyone that uses SPF is perfectly entitled to reject that mail.
The real fix would be of course to always sent invitation e-mail using a surveymonkey.com envelope address, and use the customer provider e-mail address as FROM address in the headers.
If you are a Surveymonkey employee and you are reading this, I can summarize this story: you're loosing revenue if you don't fix this.