Canary
8.4#1 in email design softwareFrom $36 a yearFree planAndroidiOSWebAPI
VisitCanary Mail suits individuals and small teams who want to manage existing email accounts across supported platforms. It is not presented as a full helpdesk system.
Mail Studio suits people creating emails who want drag-and-drop editing with reusable blocks, custom code access, or HTML export. It runs on Linux, macOS, and Windows.