Unfortunately, the hotkey to the To field only opens the address book which will more likely get in your way. You can check this out by saying press alt t or press alt tango.
The reason we built KnowBrainer and VerbalBasic II is because of Dragon's limitations but when it comes to your question, we are running into the same brick wall which seems to be new. Having said that, you you can get around this problem by creating your own commands. This is arguably Dragon's greatest strength. This would be clumsy but you could create a macro that temporarily moves the cursor to the Subject field by pressing {Alt+u} and presses {Shift+Tab 2} to move to the To field.
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