If you use Gmail or your server runs through it, you can utilize Gmail Meter.
Gmail Meter provides statistics on inbox activity each month.
Using this tool, you can see how many emails you are sending and receiving each month and how fast you respond – It also reveals other cool intricacies about your email habits.
By using Gmail Meter, I learned I get less incoming emails on Thursday and Friday, so those are typically better meeting days.
It takes less than a minute to run your report. You can save the report to spreadsheet form in case you ever want to compare the data month to month.
On another note, one of my first Tool Tuesdays was about the importance of snoozing email on important inquiries to ensure they are handled, and if not, they are returned to your inbox at a time of your choosing. The tools I recommended were for Gmail only, but here is one I found that may be useful for those of you on Outlook.