When Instagram started to become popular more than a decade ago, many bloggers abandoned their personal websites to post on the photo-sharing app instead. Those blogs and mailing lists became in vogue again as creators looked for ways to connect more personally with fans. That meant a new market for the email marketing software services that manage such outreach. 

Creator marketing startup ConvertKit has fought for its share of the action, competing with larger companies such as Mailchimp, which specializes in small businesses, as well as buzzy startups such as newsletter publisher Substack.