Add support for **Implicit TLS (SMTPS)** to the SMTP email service

[hungtcs]

The SMTP Send function only supported STARTTLS (plain connection → STARTTLS command → TLS upgrade), which works on ports like 587.
However, many SMTP servers — including Aliyun DirectMail — use port 465 with Implicit TLS (TLS handshake before any SMTP command).
The original code attempted a plain TCP connection on port 465, causing the server to reject it immediately with EOF.

Changes

app/pkg/env/env.go

• Added new config field EMAIL_SMTP_ENABLE_IMPLICIT_TLS (default: false)

app/services/email/smtp/smtp.go

• Send function now accepts an enableImplicitTLS bool parameter
• When enabled, establishes a TLS connection (tls.Dial) before any SMTP dialogue, then creates the SMTP client via smtp.NewClient
• When disabled, falls back to the original smtp.Dial + STARTTLS flow
• STARTTLS is automatically skipped when implicit TLS is active

app/services/email/smtp/smtp_test.go

• Updated mockSend signature to match the new Send function signature

Usage

Add to .env:

EMAIL_SMTP_HOST=smtp.example.com
EMAIL_SMTP_PORT=465
EMAIL_SMTP_ENABLE_STARTTLS=false
EMAIL_SMTP_ENABLE_IMPLICIT_TLS=true