Mail's SMTP setting for ssl won't turn off

I am having problems sending emails and have found it appears that in the advanced pane of the SMTP settings the checkbox that says USE SECURE SOCKETS LAYER (SSL) is always checked. Whatever I do to change it, next time I come back it is checked again.

Is there something else controlling this setting? My SMTP does definitely NOT need SSL.

I have tried using custom port, but again although it lets me uncheck the box, as soon as I try to send the mail there are problems and looking at this pane again I find the SSL is once again checked.

I have tried adding a new SMTP server, but as soon as I change the popup to PASSWORD it refuses to let me uncheck the box.

Any ideas?