Some mails that I write I expect to receive a reply to, but also accept that it may take some time before I receive a reply. An example would be a mail I write to the local council. Other mails I may or may not get a reply to. It would be nice to have a list of all the mails that I have sent that I expect a reply to, to help me manage reminders when necessary etc. I could do this with e.g. an external spreadsheet but it would be nice to have such a facility integrated with claws. The way I envisage such a facility would be a list, popped up either from a menu or from a button at the top of the compose window. The menu would allow me to access the list to review entries and manage them. The compose window button would cause the current mail being composed to be added to the list, as would checking the Request Return Receipt menu item. Maybe it would be possible to set a time limit for a reply to a particular email. Clearing a reply-expected flag should be manual, since something like an automatic read receipt shouldn't count as a reply. I'd be interested to know if anybody thinks this is a good (or bad) idea.
You can use tags to mark your mails, for which you want to check for a reply. Give your sent email a specific tag like "wfr" (waiting for reply) and filter your SENT-folder for that tag to get a list of emails you want to check for a reply. As a bonus, you could set up a processing rule to set an orange color for emails which have the wfr tag AND are older than 3 days and a red color for older than 2 weeks. When you receive a reply on your email, just remove the tag.