However, your service is not worth over three times the cost I am currently paying to keep track of my internet bookmarks.
But I also realize I am a bit of an outlier. I host my own music server rather than use Spotify. I run my own Nextcloud service rather than use Dropbox. I run my own Plex server rather than subscribe to Netflix. I cancelled my Amazon Prime after they raised the price. I didn't use their streaming services and I can wait another day or two for the junk I just bought.
Hopefully this info will help you and your company.
Think about how Apple Pay solves this problem: they give a unique email address to every site. People who have their own domains, or who trust the base+suffix@domain approach and don't think sites will strip off the +suffix, do something similar manually.
You could provide a similar service for sites that don't accept Apple Pay.
Provide an automatic email address (no per-site setup required) for people who expect a few transactional mails ("here's your shipment tracking number"), track (across customers) whether those email addresses get sold to spam lists, flag companies that get caught selling email addresses.
If you're providing the insulating layer on email, you're providing more obvious value to your customers.
I'm not affiliated to them (discovered them on Producthunt I think) but I use it all of the time for one-off eCommerce websites, newsletters, etc. you can have your own custom domain and anything before the @ is a wildcard and gets automatically created.
It is super easy to "delete" or stop the forwarding of email to these addresses
That said we've had a few sales today, so we'll see how it goes. If it doesn't work out then it's fairly easy to tweak the price, or we could offer a freemium version.
Though my instinct tells me that if users wouldn't even pay $3/m for something then it probably hasn't got great product market fit and we need to change our approach!