Improve initialization of preprocessor

src/paperless_mail/mail.py

@@ -440,10 +440,18 @@ class MailAccountHandler(LoggingMixin):
     def _init_preprocessors(self):
         self._message_preprocessors: list[MailMessagePreprocessor] = []
         for preprocessor_type in self._message_preprocessor_types:
-            if preprocessor_type.able_to_run():
+            self._init_preprocessor(preprocessor_type)
+
+    def _init_preprocessor(self, preprocessor_type):
+        if preprocessor_type.able_to_run():
+            try:
                 self._message_preprocessors.append(preprocessor_type())
-            else:
-                self.log.debug(f"Skipping mail preprocessor {preprocessor_type.NAME}")
+            except Exception as e:
+                self.log.warning(
+                    f"Error while initializing preprocessor {preprocessor_type.NAME}: {e}",
+                )
+        else:
+            self.log.debug(f"Skipping mail preprocessor {preprocessor_type.NAME}")
 
     def _correspondent_from_name(self, name: str) -> Optional[Correspondent]:
         try:

src/paperless_mail/preprocessor.py

@@ -1,4 +1,5 @@
 import abc
+import os
 from email import message_from_bytes
 from email import policy
 from email.message import Message
@@ -45,7 +46,11 @@ class MailMessageDecryptor(MailMessagePreprocessor, LoggingMixin):
 
     @staticmethod
     def able_to_run() -> bool:
-        return settings.EMAIL_ENABLE_GPG_DECRYPTOR
+        if not settings.EMAIL_ENABLE_GPG_DECRYPTOR:
+            return False
+        if settings.EMAIL_GNUPG_HOME is None:
+            return True
+        return os.path.isdir(settings.EMAIL_GNUPG_HOME)
 
     def run(self, message: MailMessage) -> MailMessage:
         if not hasattr(message, "obj"):