We have made a change, so that websmtp.simply.com port 25 now requires SMTP-AUTH, just like port 587 always has.
The change is made to avoid abuse of the service, thereby making sure that all customers will have the emails sent from their websites delivered.
More info can be found here https://www.simply.com/en/support/faq/mail/606/
The server is still only available if you are connecting from within our web servers.