Alt together some character is used as hotkey in ALL applications. Hold it down and you will see a small underline under (usually) the first character of most buttons, press this character on the keyboard and the button will be pressed. I think it would collide with S quite frequently. It is AltGr-S you are supposed to use for localized S-characters.
For Alt-S, aren't AltGr and Alt different keys on your keyboard? I use the US-International keyboard layout and the right alt-key is AltGr and the left alt-key is Alt. Sending only happens with the left key.
You have Ctrl-F as discussed which is completely different to the rest of windows.
You have alt-S for send as well which is used in some language for special characters.
And the most annoying is shift+enter. When you want a single line break in an HTMl email it sends it instead. This has a warning now.
No end of grief those have given me.