use utf-8 when unknown charset in parseaddr_unicode()

app/email_utils.py

@@ -630,6 +630,11 @@ def parseaddr_unicode(addr) -> (str, str):
             except UnicodeDecodeError:
                 LOG.warning("Cannot decode addr name %s", name)
                 name = ""
+            except LookupError:  # charset is unknown, e.g.
+                LOG.exception(
+                    "Cannot decode %s with %s, use utf-8", decoded_string, charset
+                )
+                name = decoded_string.decode("utf-8")
         else:
             name = decoded_string