use async in email handler

email_handler.py

@@ -31,6 +31,7 @@ It should contain the following info:
 
 """
 import argparse
+import asyncio
 import email
 import os
 import time
@@ -1711,7 +1712,7 @@ def should_ignore(mail_from: str, rcpt_tos: List[str]) -> bool:
     return False
 
 
-def handle(envelope: Envelope) -> str:
+async def handle(envelope: Envelope) -> str:
     """Return SMTP status"""
 
     # sanitize mail_from, rcpt_tos
@@ -1934,7 +1935,7 @@ def handle(envelope: Envelope) -> str:
 class MailHandler:
     async def handle_DATA(self, server, session, envelope: Envelope):
         try:
-            ret = self._handle(envelope)
+            ret = await self._handle(envelope)
             return ret
         except Exception:
             LOG.e(
@@ -1945,7 +1946,7 @@ class MailHandler:
             return status.E404
 
     @newrelic.agent.background_task(application=newrelic_app)
-    def _handle(self, envelope: Envelope):
+    async def _handle(self, envelope: Envelope):
         start = time.time()
 
         # generate a different message_id to keep track of an email lifecycle
@@ -1958,23 +1959,21 @@ class MailHandler:
             envelope.rcpt_tos,
         )
 
-        app = new_app()
-        with app.app_context():
-            ret = handle(envelope)
-            elapsed = time.time() - start
-            LOG.i(
-                "Finish mail from %s, rctp tos %s, takes %s seconds <<===",
-                envelope.mail_from,
-                envelope.rcpt_tos,
-                elapsed,
-            )
-            newrelic.agent.record_custom_metric(
-                "Custom/email_handler_time", elapsed, newrelic_app
-            )
-            newrelic.agent.record_custom_metric(
-                "Custom/number_incoming_email", 1, newrelic_app
-            )
-            return ret
+        ret = await handle(envelope)
+        elapsed = time.time() - start
+        LOG.i(
+            "Finish mail from %s, rctp tos %s, takes %s seconds <<===",
+            envelope.mail_from,
+            envelope.rcpt_tos,
+            elapsed,
+        )
+        newrelic.agent.record_custom_metric(
+            "Custom/email_handler_time", elapsed, newrelic_app
+        )
+        newrelic.agent.record_custom_metric(
+            "Custom/number_incoming_email", 1, newrelic_app
+        )
+        return ret
 
 
 def main(port: int):