Each sendExportEmail call created a new nodemailer transport which was never
closed, leaving the internal SMTP connection pool alive. With 3-retry backoff,
up to 3 leaked transports per invoice accumulate over time and can exhaust OS
socket limits. Add transport.close() in a finally block.
- createTransport() called per-send from DB SmtpConfig (Pitfall 3 mitigation — not at startup)
- Injects SettingsService to load decrypted SMTP config per tenant
- secure/requireTLS mapped from encryption field (ssl-tls / starttls / none)
- Auth omitted when username absent (anonymous relay support)
- Attachment contentType: application/vnd.openxmlformats-officedocument.spreadsheetml.sheet
- Error path rethrows after generic log (T-07-10) so DkvService can run 3-retry backoff (D-16)
- Does not import @nestjs-modules/mailer abstractions
schalli