Use context manager for SMTP

src/ddns_service/email.py

@@ -76,11 +76,10 @@ class EmailService:
             smtp_host = self.config["smtp_host"]
             smtp_port = self.config["smtp_port"]
 
-            server = smtplib.SMTP(smtp_host, smtp_port)
-            if self.config.get("smtp_starttls", False):
-                server.starttls()
+            with smtplib.SMTP(smtp_host, smtp_port) as server:
+                if self.config.get("smtp_starttls", False):
+                    server.starttls()
 
-            try:
                 if self.config.get("smtp_user"):
                     server.login(
                         self.config["smtp_user"],
@@ -89,8 +88,6 @@ class EmailService:
                 server.sendmail(msg["From"], [to], msg.as_string())
                 logging.info(f"Email sent: to={to} subject={subject}")
                 return True
-            finally:
-                server.quit()
 
         except Exception as e:
             logging.error(f"Email send failed: to={to} error={e}")