**Related issue:** Resolves#42288
# Summary
This PR adds support for configuring an optional SES sender domain.
When the SES email backend is enabled, Fleet can now use a configured
sender domain for the `From` address instead of always deriving the
domain from `server.server_url`. If the setting is not provided, Fleet
keeps the existing behavior.
# Impact
This gives self-hosted operators a server-side SES configuration option
for email sending without changing UI-managed SMTP settings.
# Root cause
The SES sender path only generated `do-not-reply@<server host>` from the
Fleet server URL, so there was no way to override the sender domain
through server configuration.
# Checklist for submitter
- [x] Changes file added for user-visible changes in `changes/`,
`orbit/changes/` or `ee/fleetd-chrome/changes`.
- [x] Added/updated automated tests
- [x] Setting(s) is/are explicitly excluded from GitOps
## Testing
- [x] `go test -tags full,fts5,netgo ./server/mail -run
'Test_(getFromSES|sesSender_SendEmail)$'`
- [x] `go test -tags full,fts5,netgo ./server/config -run
'TestConfig(SESSenderDomain|Roundtrip)$'`
- [x] `go test -tags full,fts5,netgo ./server/service -run
'TestService_EmailConfig$'`
- [ ] QA'd all new/changed functionality manually
<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit
* **New Features**
* Added optional SES sender domain configuration. Users can specify a
custom domain for the email "From" address via config or environment
variable; when unset it falls back to the server hostname.
* **Tests**
* Added and expanded tests to verify sender-domain precedence,
From-header generation, and related error cases.
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---------
Co-authored-by: Lucas Manuel Rodriguez <lucas@fleetdm.com>
Co-authored-by: Copilot Autofix powered by AI <175728472+Copilot@users.noreply.github.com>
