I have now been in dialogue with one.com regarding issues with sending forms from my website. You believed that the problem was on their end.
The issue has been reviewed by their 3rd level team, and they provided the following feedback:
"A review of the logs shows that the form is not sending any request to the mail server at all. This means that the error occurs before the script attempts to connect to the SMTP server.
This may indicate that the issue is at the PHP level, or that the form is not properly set up/configured."
I had that trouble when forms first come out but as I say all works ok now….try rebooting as youve changed the smtp server now,i also deleted everything from the server occasionally and upload all files
also have you got another email address you can try
im assuming you have the error and success component bits in you form