fix#14562fix#14226fix#14192
#### PR Dependency Tree
* **PR #14564** 👈
This tree was auto-generated by
[Charcoal](https://github.com/danerwilliams/charcoal)
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## Summary by CodeRabbit
* **New Features**
* SMTP and fallback SMTP name now default to empty and will use the
system hostname when not set.
* HELO hostname resolution includes stricter normalization/validation
for more reliable mail handshakes.
* **Documentation**
* Updated admin and config descriptions to explain hostname/HELO
behavior and fallback.
* **Tests**
* Added tests covering hostname normalization and rejection of invalid
HELO values.
* **Chores**
* Updated example env and ignore rules.
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## Summary by CodeRabbit
- **Chores**
- Updated the default setting for the indexer feature to be disabled by default.
- Added a sample environment variable for enabling the indexer in the example configuration file.
- Introduced a new environment variable for the indexer in the CI workflow configuration.
- **Tests**
- Adjusted test configurations to explicitly enable the indexer feature during test execution.
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DarkSky