Hi @RBanola!
In addition to the suggestions above, I’d like to point you towards this (click in number order, 1-->3)
I personally find this the most useful Email performance area of HubSpot.
The report you’re specifically looking for (replies) can be found if you scroll down a bit, you’ll find the Email Data Chart, and if you click the highlighted drop-down you can switch to Email Replies.
Of course you can add these reports to a Dashboard, especially useful if you’re sending a weekly automated dashboard snapshot to stakeholders off-platform.
One point you raised is best practice regarding measuring performance.
Personally, I wouldn’t advise anyone to measure replies from Marketing emails. It’s not unheard of, but replies would usually be an expected KPI on one-to-one emails, rather than mass marketing emails.
Think about what action you’re trying to drive, and what value you’re delivering in exchange. Are you delivering value at every step? If your CTA is “Reply to this email”, perhaps you’re not giving yourself enough opportunity to delight your customers. And going the other way, you don’t have as much data to measure how effective your campaign is.
If you have a CTA to click through to a landing page, you have two opportunities to deliver value (value within the email, and value on the landing page). And then you have a further opportunity to drive a conversion by offering yet more value, in the form of a meeting with one of your team. Suddenly you have 3x datapoints to measure (Opened, Opened + Clicked Through, Opened + Clicked Through + Booked).
That said, of course, if it works for you then it’s a good idea 
Thanks for the tag in @BérangèreL!
and have a fabulous day!
