add ip change notification and refine sender display

app/services/email.py

@@ -1,7 +1,9 @@
 from __future__ import annotations
 
 from dataclasses import dataclass
+from datetime import UTC, datetime
 from email.message import EmailMessage
+from email.utils import formataddr
 import smtplib
 
 from app.config import Settings
@@ -21,6 +23,7 @@ class SMTPConfig:
     port: int
     username: str
     password: str
+    from_name: str
     from_address: str
     to_address: str
     use_starttls: bool
@@ -47,6 +50,7 @@ def get_smtp_config(settings: Settings, *, require_enabled: bool = True) -> SMTP
         port=settings.smtp_port,
         username=settings.smtp_username,
         password=settings.smtp_password,
+        from_name=settings.smtp_from_name,
         from_address=settings.smtp_from_address,
         to_address=settings.smtp_to_address,
         use_starttls=settings.smtp_use_starttls,
@@ -72,7 +76,7 @@ def send_plaintext_email(
     smtp_config = get_smtp_config(settings, require_enabled=require_enabled)
     message = EmailMessage()
     message["Subject"] = subject
-    message["From"] = smtp_config.from_address
+    message["From"] = _build_from_header(smtp_config)
     message["To"] = recipient or smtp_config.to_address
     message.set_content(body)
 
@@ -84,7 +88,11 @@ def send_plaintext_email(
                 smtp.ehlo()
             if smtp_config.username:
                 smtp.login(smtp_config.username, smtp_config.password)
-            smtp.send_message(message)
+            smtp.send_message(
+                message,
+                from_addr=smtp_config.from_address,
+                to_addrs=[recipient or smtp_config.to_address],
+            )
     except (OSError, smtplib.SMTPException) as exc:
         error_message = _sanitize_error_message(str(exc), smtp_config.password)
         raise EmailDeliveryError(error_message or "SMTP delivery failed") from exc
@@ -99,8 +107,43 @@ def send_smtp_test_email(settings: Settings) -> None:
     )
 
 
+def send_public_ip_changed_email(
+    settings: Settings,
+    *,
+    previous_ipv4: str,
+    current_ipv4: str,
+    detected_at: datetime,
+) -> None:
+    send_plaintext_email(
+        settings,
+        subject="Public IP changed",
+        body=(
+            "Your public IPv4 address has changed.\n\n"
+            f"Previous IP: {previous_ipv4}\n"
+            f"Current IP: {current_ipv4}\n"
+            f"Detected at: {_format_utc_timestamp(detected_at)}\n\n"
+            "If you use Namecheap API trusted IP restrictions, you may need to "
+            "update the trusted IP manually.\n"
+        ),
+    )
+
+
 def _sanitize_error_message(message: str, password: str) -> str:
     sanitized = message
     if password:
         sanitized = sanitized.replace(password, "[redacted]")
-    return sanitized
+    return sanitized
+
+
+def _format_utc_timestamp(value: datetime) -> str:
+    if value.tzinfo is None:
+        normalized = value.replace(tzinfo=UTC)
+    else:
+        normalized = value.astimezone(UTC)
+    return normalized.strftime("%Y-%m-%d %H:%M:%S UTC")
+
+
+def _build_from_header(smtp_config: SMTPConfig) -> str:
+    if smtp_config.from_name:
+        return formataddr((smtp_config.from_name, smtp_config.from_address))
+    return smtp_config.from_address