It happened the same to me, I have been looking already for a month of ways to solve the problem, it identifies everything as spam, so for few people on my website it works, but on mobile devices it identifies almost everything as spam and the email is not sent. Looks like people are not even able to press the send button. I had a look on blogs and so on, to find ways to solve the problem, so it mostly said that since the border of the button turned orange, it was because it was getting it a spam so that I should configure it, to put the recaptcha and so, I did, but I still have the problem. It is not the SMTP, which I solved a year ago or so, because the emails where not being sent or they took hours or days to arrive.
I understand what you said about having it without paying a penny, and I agree with that, I mean , what Yordan said, so I was looking for an alternative even if I have to pay, because my business is not working anymore for that.