This is a maintenance release with a couple of bug fixes, coding standard changes, and a major overhaul to the testing system.
- Use shorter Message-ID headers (with more entropy) to avoid iCloud blackhole bug
- Switch to Symfony code style (though it's not well defined)
- CI builds now apply syntax & code style checks, so make your PRs tidy!
- CI code coverage only applied on latest version of PHP to speed up builds (thanks to @Slamdunk for these CI changes)
- Remove
composer.lock- it's important that libraries break early; keeping it is for apps - Rename test scripts to PSR-4 spec
- Make content-id values settable on attachments, not just embedded items
- Add SMTP transaction IDs to callbacks & allow for future expansion
- Expand test coverage