add local hostname setting

docs/getting-started.md

@@ -32,6 +32,7 @@ class has following attributes
 -  SUPPRESS_SEND:  To mock sending out mail, defaults 0.
 -  USE_CREDENTIALS: Defaults to `True`. However it enables users to choose whether or not to login to their SMTP server.
 -  VALIDATE_CERTS: Defaults to `True`. It enables to choose whether to verify the mail server's certificate
+-  LOCAL_HOSTNAME: It enables to set the hostname of the local machine, which is used to connect to the SMTP server.
 
 
 ### ```MessageSchema``` class

fastapi_mail/config.py

@@ -21,6 +21,7 @@ class ConnectionConfig(Settings):
     USE_CREDENTIALS: bool = True
     VALIDATE_CERTS: bool = True
     TIMEOUT: int = DEFAULT_TIMEOUT
+    LOCAL_HOSTNAME: Optional[str] = None
 
     def template_engine(self) -> Environment:
         """

fastapi_mail/connection.py

@@ -39,6 +39,7 @@ async def _configure_connection(self) -> None:
                 use_tls=self.settings.MAIL_SSL_TLS,
                 start_tls=self.settings.MAIL_STARTTLS,
                 validate_certs=self.settings.VALIDATE_CERTS,
+                local_hostname=self.settings.LOCAL_HOSTNAME,
             )
 
             if not self.settings.SUPPRESS_SEND:  # for test environ