If you send an important email, then go to the Sent folder and hit the 1 key with the email highlighted. This will tag it as Important.
Create a search folder by right-clicking the Sent folder and choosing Search, then at the bottom choose Save as Search Folder
Give the folder a good name "Sent Important", and create as a sub-folder of whatever makes sense to you.
Click the Choose.. button and confirm that only the Sent folder is ticked.
Change the first drop-down to read Tags, and make sure the condition is "Important".
Click Create.
Now you will have a folder containing all your important Sent items. If you want to mark one as dealt with, you just hit 1 on it again, which will remove the important tag.
Couldn't automatic resend without human control be potentially embarrassing in some situations? – harrymc – 2012-02-27T20:40:43.927
Yes. What I haven in mind would be that it automatically opens a re-send mail and I just press send. But I could not get any kind of reminder sending to work. The only thing I see is that some reminder text can be set, but I have no clue where it is used. – Alex – 2012-02-27T20:54:34.580