Hi Eleanor,
Thanks so much for this feedback!
To understand if you are getting more emails each day than you can keep up with, I have a few metrics I can recommend:
To monitor your email volume
Busiest Hours
A heatmap showing your busiest hours throughout the day over your report period. This can help you identify at what times you are receiving the most emails, as well as what time you are at your most productive.

Messages by Day
A breakdown of your message volume, showing both sent and received over each day of the report period. This allows you to see which days you were the busiest over the month, so you can identify patterns and plan accordingly.

To understand how well you are keeping up with your email volume
Response Time
Both your quickest response time and your average time taken before your first response are shown, as well as a graph to help you visualise how long first responses took.
If you are taking too long to reply to emails, this could be an indication that you are receiving too many.

Emails Replied
The number of sent emails you received/did not receive a reply to.
The number of received emails you replied/did not reply to.
This effectively measures your response rate, if you have a large volume of unreplied emails this could signify that you are receiving too many.

Top Interactions
The email addresses / domains which you interacted with the most, along with:
Number of messages exchanged (broken down into sent and received).
Best contact time, determined by when that contact most often emails you, and is therefore most likely to be looking at their inbox. This means they will be more likely to see your email before it is buried under any subsequent emails.
Your average response time to that contact/domain.
You can switch between individual email addresses or domains in the top right.
This should allow you to see which contacts or domains you are spending the most time emailing, or identify which communications are one-sided.

I hope this helps you quantify your email volume and how well you are keeping up.
Others in your company are most welcome to sign up for Email Meter, so you can compare!
We also have a Teams feature which allows a number of inboxes to be monitored from one central dashboard.
Please let me know if you have any further questions I will be happy to suggest how best you can proceed with Email Meter to streamline your productivity!
Thanks,
Gino