Excellent, seems there is no other reply reminder out there Rated 5 out of 5 stars

Perfect, this plug-in helps to keep track of e-mail requests that expect a reply. Thank you for the good work. Here are some ideas, but the plug-in is already useful as it is now. 1) the calendar entry says: "undefined" is expecting replies, I don't know why it say "undefined" instead of, for instance, the subject of the e-mail or the involved parties 2) it would be great to have a link from the calendar entry to the e-mail for which the alert was triggered

This review is for a previous version of the add-on (0.4). 

Some bug might caused undefined to be displayed. It is intended to show the subject of the email. Could you please provide me with the subject of that email so that I could check what caused the problem.
For the link function, I have an implementation in mind but it requires some alteration to the UI. I'll get to it when I have more time (during school holidays maybe) :)