decode the subject

app/email_utils.py

@@ -593,6 +593,17 @@ def get_spam_from_header(spam_status_header, max_score=None) -> (bool, str):
     return spamassassin_answer.lower() == "yes", spam_status_header
 
 
+def get_header_unicode(header: str):
+    decoded_string, charset = decode_header(header)[0]
+    if charset is not None:
+        try:
+            return decoded_string.decode(charset)
+        except UnicodeDecodeError:
+            LOG.warning("Cannot decode header %s", header)
+
+    return header
+
+
 def parseaddr_unicode(addr) -> (str, str):
     """Like parseaddr() but return name in unicode instead of in RFC 2047 format
     Should be used instead of parseaddr()

email_handler.py

@@ -100,6 +100,7 @@ from app.email_utils import (
     is_valid_alias_address_domain,
     should_add_dkim_signature,
     add_header,
+    get_header_unicode,
 )
 from app.extensions import db
 from app.greylisting import greylisting_needed
@@ -700,6 +701,7 @@ def forward_email_to_mailbox(
         if mailbox.generic_subject:
             LOG.d("Use a generic subject for %s", mailbox)
             orig_subject = msg["Subject"]
+            orig_subject = get_header_unicode(orig_subject)
             add_or_replace_header(msg, "Subject", mailbox.generic_subject)
             msg = add_header(
                 msg,