Answer
The remote system issued a EXPN command to GMS but GMS the list server has not been installed. GMS has rejected the command.
In this case session Undefined was processing a connection from the server/client at Undefined when it received the command
Undefined
so GMS responded with
560 No list server key.
This problem is most likely to be caused by someone who is attacking your system in an attempt to find a weakness. This potential attack has been identified by GMS and ignored. To find out why this is being done, contact the owner of the IP address Undefined and ask them.
See Also:
- How do I contact the owner of a remote server?
- What is the SMTP EXPN command?
- What is SMTP Response Code Theory?
- How do alerts work?
- How do I contact the owner of a client?
Keywords:EXPN list server key attack 8113