- Substantial revision of DKIM header generation
- Use shorter hashes for auto-generated CID values
- Fix format of content-id headers, and only use them for inline attachments
- Remove all use of XHTML
- Lots of coding standards cleanup
- API docs are now auto-updated via GitHub actions
- Fix header separation bug created in 6.1.1
- Fix misidentification of background attributes in SVG images in msgHTML