* fix: join multiple Reply-To addresses as comma-separated string
Some SMTP providers (e.g., SendLayer) reject emails when Reply-To is
passed as an array to nodemailer, which serializes it as multiple
Reply-To headers. Using a comma-joined string is RFC 2822 compliant
and works universally across all SMTP providers.
Fixes#28610
* test: add unit tests for getReplyToHeader SMTP compatibility
- Verify replyTo is always returned as comma-separated string, not array
- Test single email, multiple emails, and empty email cases
- Add RFC 5322 compliance test for SMTP compatibility
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
* docs: add RFC 5322 reference comment to getReplyToHeader tests
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
---------
Co-authored-by: Lawrence Christian <67164412+LCNDevs@users.noreply.github.com>
Co-authored-by: Romit <85230081+romitg2@users.noreply.github.com>
Co-authored-by: Romit <romitgabani1.work@gmail.com>
Co-authored-by: Claude Opus 4.5 <noreply@anthropic.com>
