Read extra headers for mail from config

check.py

@@ -2,6 +2,8 @@
 
 """Check if conference websites are live."""
 
+import configparser
+import os
 import re
 import smtplib
 import warnings
@@ -9,7 +11,17 @@ from email.mime.text import MIMEText
 from email.utils import formatdate, make_msgid
 
 import requests
-from urllib3.exceptions import InsecureRequestWarning
+from urllib3.exceptions import InsecureRequestWarning  # type: ignore
+
+config_file_path = os.path.expanduser(
+    os.path.join(
+        os.getenv("XDG_CONFIG_HOME", "~/.config"), "conference-check", "config"
+    )
+)
+
+config = configparser.ConfigParser()
+config.read(os.path.expanduser(config_file_path))
+
 
 # Suppress only the single InsecureRequestWarning from urllib3
 warnings.filterwarnings("ignore", category=InsecureRequestWarning)
@@ -102,6 +114,10 @@ def send_mail(subject: str, body: str) -> None:
     msg["Date"] = formatdate()
     msg["Message-ID"] = make_msgid()
 
+    # extra mail headers from config
+    for header_name, value in config["mail_headers"].items():
+        msg[header_name] = value
+
     s = smtplib.SMTP(SMTP_HOST)
     s.sendmail(mail_from, [MAIL_TO_ADDRESS], msg.as_string())
     s.quit()