When sending an Email withing a tab inside a session, I need an event to register my custom functionality on. Based on some checks, it should close the whole session as well.

The problem is, I can't register this code on the OnSave. OnSave is called when the user presses send, but if I were to close the session then, the send would not be done after the save.

The idea is to have an event handler to register code on, which triggers just before the tab is closed, but not too early to cancel the send (or what ever other action leads to closing of the tab).