Out of interest I tried accessing the iCloud website using Safari 4.1.3 on 10.4.11; I got a warning that it was an unsupported browser and was able to log into it and go to Mail. I was also able to send a message successfully, but be warned that it is very slow - opening the New Message pane took around a minute of spinning beachball, so don't panic and think it's crashed - just wait it out.
If you can get into Mail and send a message then that would prove your account itself is OK.
First of all, thank you Richard for spending extra time on testing if sending mail in system 10.4.11 works after September 25, 2013. I really appreciate you did this because I was convinced that the pre - Intel computers had been abandoned by Apple . . .
To summon up:
My set-up is - and has been - 100% as advised by Apple. If I made screen dumps they would be the same as made by Roger
I have no problems sending via Icloud.com, but it is to slow to be an option, but when travelling its OK
I used Mac Mail to all test’ of sending mail, but it makes no difference, it returns the ususal message 5.7.8
I use Hotmail, Gmail, and various other mail servers - all with SSL and security functions – they all work with no problems.
End of story