Use SMTP_HELO_HOST for the initial HELO on SMTP conns

Mailman/Handlers/SMTPDirect.py

@@ -61,7 +61,8 @@ class Connection:
         self.__conn = None
 
     def __connect(self):
-        self.__conn = smtplib.SMTP()
+        self.__conn = smtplib.SMTP(
+            local_hostname=mm_cfg.SMTP_HELO_HOST)
         self.__conn.set_debuglevel(mm_cfg.SMTPLIB_DEBUG_LEVEL)
         self.__conn.connect(mm_cfg.SMTPHOST, mm_cfg.SMTPPORT)
         if mm_cfg.SMTP_AUTH: