I have 9 different email accounts set up in Microsoft Outlook (mostly free Google Apps IMAP accounts), and while it works great for receiving and replying to messages, I have found myself often sending from the “default account” in Outlook rather than the account I meant to send from. The reason is that when you compose a new message, if you do not select the Account, it uses the default one.
I really wanted to force Outlook to prompt me for the account to use when sending email, but after some searching, it appears that is not possible. Maybe it will be in the next version of Outlook.
The best option I could find was to set up deferred delivery in Outlook. This cause Microsoft Outlook to delay sending your email for a specified number of minutes (I chose 5 minutes). While this is not an ideal solution, it does allow me to quickly go in and change the ones that I remember – usually right after I send them. So, it’s better than nothing, plus it allows me to pull back emails that I may have written too hastily as well.