feat: switch email delivery from Resend to SMTP with libcurl integration

README.md

@@ -9,7 +9,7 @@ Install native build dependencies first. On Ubuntu:
 
 ```bash
 sudo apt install build-essential cmake ninja-build git pkg-config \
-  libjsoncpp-dev uuid-dev zlib1g-dev libssl-dev \
+  libcurl4-openssl-dev libjsoncpp-dev uuid-dev zlib1g-dev libssl-dev \
   libmariadb-dev libmariadb-dev-compat
 ```
 
@@ -95,18 +95,29 @@ The app serves the generated JSON at `/api/v1/openapi.json` and Swagger UI at
 
 ## Email Delivery
 
-OTP delivery uses Resend HTTP API through Drogon's async `HttpClient`.
-Set these environment variables before starting backend:
+OTP delivery uses SMTP through `libcurl`. Local dev defaults to Mailpit.
+Set these environment variables before starting backend for local Mailpit:
 
 ```bash
-export MAIL_PROVIDER=resend
-export RESEND_API_BASE_URL=https://api.resend.com
-export RESEND_API_KEY=re_xxx
+export MAIL_PROVIDER=smtp
+export SMTP_HOST=127.0.0.1
+export SMTP_PORT=1025
 export MAIL_FROM=[email protected]
 ```
 
-Mailpit can still run locally for manual inspection or future integrations, but
-current backend OTP flow no longer speaks SMTP directly.
+For Resend in production, use SMTP credentials instead:
+
+```bash
+export MAIL_PROVIDER=resend
+export SMTP_HOST=smtp.resend.com
+export SMTP_PORT=465
+export SMTP_USERNAME=resend
+export SMTP_PASSWORD=re_xxx
+export SMTP_USE_TLS=true
+export SMTP_VERIFY_PEER=true
+export SMTP_VERIFY_HOST=true
+export MAIL_FROM=[email protected]
+```
 
 ## Visione Lab
 
@@ -157,7 +168,7 @@ multi-architecture Mailpit image to avoid `exec format error` failures on ARM
 servers.
 
 Set `DB_NAME`, `DB_USER`, `DB_PASSWORD`, `MYSQL_ROOT_PASSWORD`,
-`RESEND_API_KEY`, `MAIL_FROM` and
+`SMTP_PASSWORD`, `MAIL_FROM` and
 `CORS_ALLOWED_ORIGIN` in Dokploy environment variables. Use the exact browser
 origin without quotes or a trailing slash, for example
 `https://visione.studentindipendenti.it`.