We use https://missiveapp.com/ It works great for our small business with only three users. we get dozens and dozens of emails every day. There are options to assign emails, share various inboxes such as sales@, info@ etc... there is also the ability to comment on emails within our team which had been very useful. It might be a great fit for you.
At the beginning the founders got customers by posting posting on different tech discovery communities like ProductHunt. But it's important to note that it took them around a few years before getting the first paying customers. Right now most new customers come from word-of-mouth and SEO content.
There's more detail in the blog post. I just a made a summary of it.
Name: Missive
Website https://missiveapp.com/
Pitch: Collaborative email app. AKA Slack + GMAIL
Details: Why? As a small team of bootstrappers, we experienced the painful reality of managing hundreds of emails a day all alone each in our own separate inbox. Never knowing if a team member has seen an email or started to act on it, having to switch context back to our chat app to get feedback on how we should respond to a particular email, or even launching Google Docs to collaboratively write an important email, it all adds up to an incredible amount of lost time.
To solve this, we added three core features to the usual email experience: shared conversations, comments and collaborative drafts.
Be it customer support, sales, partnerships or notifications, in our experience, email often requires more than two eyeballs. Missive makes that process efficient.
Looking for: Beta testers! OSX native app coming in a few days.
Discount: It is free during closed beta. 1 month messages limit history.
Know more https://missiveapp.com/blog/hello-world & https://missiveapp.com/blog/improving-your-team-email-productivity-with-missive