Email marketing

For techies: - Great. But has a fatal flaw in editor: easy to run out of previews very quickly. - Great. Unlimited previews! - Cheaper $25/mo, but does not test Gmail on iPhone, which is a common one! So disqualified!
There’s also the powerful, but it’s too expensive and complicated unless you actually need the other features they offer, besides just epreviews.

For non-techies:

Hubspot - best email builder and CRM
LemList - nice easy to use CRM platform
Mautic - open source self-hosted email marketing platform - build beautiful emails, easily
SalesHandy for email OMG, this is a must have! Or something similar. Get something similar. Know if/when the email you sent is opened and read! Know if/when a link in the email was clicked!