That RFE is fixed in the upcoming ZCS 5.0.14 (and subsequent future ZD releases).
The new keys are:
CTRL+S: save draft
CTRL+Enter: send message
Currently you can set:
/opt/zimbra/mailboxd/webapps/zimbra/WEB-INF/classes/keys/ZmKeys.properties (or respective language)
zmmailboxdctl restart
Code:
compose.Save.display = Ctrl+S
compose.Save.keycode = Ctrl+83
compose.Save.description = Save draft
compose.Save.sort = 30030
compose.Send.display = Ctrl+Enter
compose.Send.keycode = Ctrl+13
compose.Send.description = Send
compose.Send.sort = 30010
Others of interest include:
Code:
options.Save.display = Ctrl+S
editContact.Save.display = Ctrl+S
editPage.Save.display = Ctrl+S
editTask.Save.display = Ctrl+S
editAppointment.Save.display = Ctrl+S