They're also bootstrapped and independent. They have a really easy to use API[2] (other providers have horrifically inscrutable APIs[3]). The customer service used to be excellent since you were talking directly to the founders. Now they've outsourced customer support so that's not as good, but I still like them far more than any other email service provider.
[0] https://emailoctopus.com/pricing-connect
[1] https://emailoctopus.com/pricing
Postmark has been doing bulk emailing since 2019.
> Q: How will you maintain high deliverability for transactional email?
> A: Separating transactional traffic from other types of email using different sending IPs and From domains is a longstanding best practice for ensuring optimal deliverability.
...
> That means transactional and broadcast traffic never intersect in Postmark, including IP ranges.
https://postmarkapp.com/blog/api-bulk-the-final-frontier#how...
† now owned by Twilio
Source: https://community.constantcontact.com/t5/Get-Help/Billing-FA...
While I also would prefer email to be text only, it seems most of the world feels differently. So I stopped worrying about it.
Side note: In theory an HTML email can be more visibly respectful of privacy while being nicely formatted, than visiting a webpage, although in practice that distinction seems increasingly rare.