Sophos XG - Internal Server Error

Hi

- Since few weeks, we experience sometimes "Internal Server Error"

Sophos send an NDLR to the sender :


- Sophos XG Firewall was unable to send the following mail:

Some text

XXX@XX.COM - Internal Server Error


How can we debug this to understand the source of the problem ?

- What we can see in awarrensmtp.log logs :

ERROR     Nov 13 13:52:47 [0x2016b987]: SER.io_handler = NULL, means read event not expected from this fd
ERROR     Nov 13 13:52:47 [0x2016b987]: SER.io_handler = NULL, means read event not expected from this fd
MESSAGE   Nov 13 13:52:48 [3741346624]: Notification generated for Mail sending failure: Recipient bla@bla.com, Mail server IP:25
MESSAGE   Nov 13 13:52:48 [3742395200]: forward_mail(): Sending Notification to 'bla@bla.com' on 'IP:25' (ipv6: '0')

- Information about Sophos XG :

SFOS 17.5.8 MR-8