Suggestion: when sending the original email, use a subject line that's meaningful both to you and to the other person, so no need to change it later. Then, bcc it directly into an email inbox which is a waiting-for list (or whatever you need it to be) -- no need to move it later. You might put a keyword in the subject line (e.g. "WF" meaning "waiting for" -- unless that will have your recipients puzzling over the acronym) and have your email system recognize that and put it straight into the appropriate box. Other emails could be keyed to go straight into an "action" folder or something.

You could use subject lines like "Please send me sales report (to self: for analysis at yearly meeting)" or be more cryptic: "Please send me sales report (myfile: YM)"