I have the same send-first-think-later problem sometimes – I ended up hunting round for an app which could intercept outgoing emails to give me a chance to review (also useful as I have about five outgoing email accounts, and sometimes I send via the wrong one the first time).

I ended up finding an app called SoftX Email Monitor – it’s designed to watch for any and all outgoing emails (to flag up spammy applications, etc), but a side effect of this is that whenever you send an email in Outlook (without whitelisting the application) it will show the email. It’s one more click to send the email (otherwise it blocks it) but it’s saved me quite a few times now! If you hit Block Send, the Send/Receive times out in Outlook and you can just open the email up, modify it / change the outgoing account etc, and then send/receive again.

It’s freeware, and works like a charm. A useful alternative to setting up a rule if you want more detailed control on a per-email basis. You can get the app from http://www.softx.org/e-monitor.html

(not affiliated with SoftX, just a happy user and recommender!)