Fix SMTP configuration to use Cloudron mail relay

Use Cloudron's internal mail relay at 172.18.0.1:2525 instead of
external SMTP server to fix email sending timeouts during registration.

start.sh

@@ -122,18 +122,11 @@ HASH_KEY_FILE="$SECRETS_DIR/hash_key"
 JWT_SECRET_FILE="$SECRETS_DIR/jwt_secret"
 SESSION_SECRET_FILE="$SECRETS_DIR/session_secret"
 
-SMTP_HOST="${CLOUDRON_MAIL_SMTP_SERVER:-}"
-SMTP_PORT="${CLOUDRON_MAIL_SMTP_PORT:-25}"
-SMTP_ENCRYPTION="${CLOUDRON_MAIL_SMTP_ENCRYPTION:-}"
-if [ -n "${CLOUDRON_MAIL_SMTPS_PORT:-}" ]; then
-  SMTP_PORT="${CLOUDRON_MAIL_SMTPS_PORT}"
-  SMTP_ENCRYPTION="tls"
-  if [ -n "${CLOUDRON_MAIL_DOMAIN:-}" ]; then
-    SMTP_HOST="mail.${CLOUDRON_MAIL_DOMAIN}"
-  fi
-fi
-SMTP_USERNAME="${CLOUDRON_MAIL_SMTP_USERNAME:-}"
-SMTP_PASSWORD="${CLOUDRON_MAIL_SMTP_PASSWORD:-}"
+SMTP_HOST="172.18.0.1"
+SMTP_PORT="2525"
+SMTP_ENCRYPTION=""
+SMTP_USERNAME=""
+SMTP_PASSWORD=""
 SMTP_EMAIL="${CLOUDRON_MAIL_FROM:-no-reply@$RP_ID}"
 SMTP_SENDER_NAME="${CLOUDRON_MAIL_FROM_DISPLAY_NAME:-Ente}"