count number of emails

I have a website with a contact form. The contact form submits to my gmail. I have never deleted any email.
I need to chart how many emails I have received in the past 3 years, so that I can find out if my number of leads have been increasing or decreasing.

I need data in this format to make the chart:
date: number of emails
January 1: 12 emails
January 2: 5 emails
January 3: 7 emails

if it can't be done by day, I can also do larger intervals like weeks or months.

anyone know how I can do this?

You could use Thunderbird to access your Gmail account then archive the messages into years and months
https://support.mozilla.org/en-US/kb/archived-messages

That is very helpful. I use thunderbird but I've never used that feature before. I always do them manually.