Is it possible to update a newsletter made in hubble via an automation tool such as Zapier/Integromat? Otherwise is it possible to add content automatically from an API to the newsletter?
We do provide an API to interact with Marketing Emails in your Portal - This is assuming the email you'r referencing is a blog subscription email for example or a basic marketing email you're using as a newsletter.
In this case, our Update a marketing email endpoint will allow you to make basic updates but should the template use the subscription format, the content in this email is controlled by a default HubSpot module and cannot be edited via the API.
To see the extent of what you can achieve via our Marketing Email API, take a look at our documentation here.