How do you permanently switch off the SSL box in Mac Mail Accounts advanced

I am having problems again with my ISP ( TalkTalk) and MacMail. This has been on and off for weeks. Presently it is with sending emails. They won't go. An error message tells me the server is offline. However, fiddling around with the account settings I find that for my (TalkTalk) account I am not supposed to tick the SSL box in Accounts/Advanced. I am told it shouldn't be checked. I can manually uncheck it, but the moment I close down the Accounts box ( and there is no instruction coming up to Save Changes) - I then find the email still won't go as the server is shown as offline. I then go to check the settings again and I find the SSL box has somehow checked itself. TalkTalk tell me that the SSL box should not be checked. Can anyone explain how to switch the thing off? I have also been having problems with my iCloud account - where the mail hasn't been sent because the server is 'offline'. However I am still receiving emails in both cases. Any advice please? Many thnks