It is the other side of the edit rate: if a quarter of drafts are edited, the rest went out unchanged. The difference is the question each number answers. The sent-unchanged rate asks “how often could I just press send?”, which is the time you actually save.
Why it matters
Vendor numbers such as a resolution rate are counted by the vendor, under a definition the vendor chooses. The sent-unchanged rate is counted from what you did with each draft, email by email, in your own inbox. It is also the number to watch before trusting a tool with more: when drafts for one kind of email are almost always sent unchanged, that kind of email needs less review.
Track it per kind of email and week by week. One overall number hides the difference between order questions, which may be easy, and complaints, which may not be.
An example
In a week, thirty of forty drafts were sent as written. The sent-unchanged rate is three out of four, and the ten edits tell you where to look.
In ReplyPen: Reports show how many Drafts you sent unchanged and how many you edited, week by week. More in the sent-unchanged rate.