make DKIM_PRIVATE_KEY_PATH optional

app/config.py

@@ -147,14 +147,15 @@ DISABLE_ALIAS_SUFFIX = "DISABLE_ALIAS_SUFFIX" in os.environ
 # the email address that receives all unsubscription request
 UNSUBSCRIBER = os.environ.get("UNSUBSCRIBER")
 
-DKIM_PRIVATE_KEY_PATH = get_abs_path(os.environ["DKIM_PRIVATE_KEY_PATH"])
 DKIM_SELECTOR = b"dkim"
-
-with open(DKIM_PRIVATE_KEY_PATH) as f:
-    DKIM_PRIVATE_KEY = f.read()
-
-
 DKIM_HEADERS = [b"from", b"to"]
+DKIM_PRIVATE_KEY = None
+
+if "DKIM_PRIVATE_KEY_PATH" in os.environ:
+    DKIM_PRIVATE_KEY_PATH = get_abs_path(os.environ["DKIM_PRIVATE_KEY_PATH"])
+    with open(DKIM_PRIVATE_KEY_PATH) as f:
+        DKIM_PRIVATE_KEY = f.read()
+
 
 # Database
 DB_URI = os.environ["DB_URI"]

app/email_utils.py

@@ -385,18 +385,19 @@ def add_dkim_signature(msg: Message, email_domain: str):
 
     # Specify headers in "byte" form
     # Generate message signature
-    sig = dkim.sign(
-        to_bytes(msg),
-        DKIM_SELECTOR,
-        email_domain.encode(),
-        DKIM_PRIVATE_KEY.encode(),
-        include_headers=DKIM_HEADERS,
-    )
-    sig = sig.decode()
+    if DKIM_PRIVATE_KEY:
+        sig = dkim.sign(
+            to_bytes(msg),
+            DKIM_SELECTOR,
+            email_domain.encode(),
+            DKIM_PRIVATE_KEY.encode(),
+            include_headers=DKIM_HEADERS,
+        )
+        sig = sig.decode()
 
-    # remove linebreaks from sig
-    sig = sig.replace("\n", " ").replace("\r", "")
-    msg["DKIM-Signature"] = sig[len("DKIM-Signature: ") :]
+        # remove linebreaks from sig
+        sig = sig.replace("\n", " ").replace("\r", "")
+        msg["DKIM-Signature"] = sig[len("DKIM-Signature: ") :]
 
 
 def add_or_replace_header(msg: Message, header: str, value: str):

example.env

@@ -70,7 +70,7 @@ EMAIL_SERVERS_WITH_PRIORITY=[(10, "email.hostname.")]
 # POSTFIX_SERVER=my-postfix.com
 
 # the DKIM private key used to compute DKIM-Signature
-DKIM_PRIVATE_KEY_PATH=local_data/dkim.key
+# DKIM_PRIVATE_KEY_PATH=local_data/dkim.key
 
 # delete and recreate the sqlite database, for local development
 RESET_DB=true