SMTP test where TCP connection opens but immediately dropped?

I have various servers which I am checking for SMTP servers running or not running. This all works fine if there is or isn't a service listening on the port. The problem comes with Windows boxes which are running an SMTP server for localhost relay only but it allows connection from the LAN but drops the connection immediately. It would apply to any kind of service that is using a libwrap style client IP check which relies on opening the TCP connection to determine the client IP address and then denying access. This shows up as a yellow if I specify smtp or red for !smtp.

Is there a way to test for a TCP connection which immediately drops as a green? For this case, I want to be alerted if the server does start accepting SMTP connections. It's effectively the opposite of smtp:s. Maybe defined something new in bb-services? There doesn't seem to be a lot of options on the expected response string - substring of the response received looks like that's all, no option to check response length for example. green on zero response length and red for refused or non-zero length would be ideal. How about smtp:z ?

My testing shows the following reports for the various cases:

• no smtp server running - smtp = red, !smtp = green, smtp:s =red, !smtp:s =green $ nc -v nosmtp 25 </dev/null nosmtp.ausport.gov.au [10.x.x.x] 25 (smtp) : Connection refused $ telnet nosmtp 25 Trying 10.x.x.x... telnet: connect to address 10.x.x.x: Connection refused telnet: Unable to connect to remote host: Connection refused

• smtp server running - smtp = green, !smtp = red, smtp:s =yellow, !smtp:s =red $ nc -v smtp 25 </dev/null smtp.ausport.gov.au [10.x.x.x] 25 (smtp) open 220 smtp.ausport.gov.au ESMTP $ telnet smtp 25 Trying 10.x.x.x... Connected to smtp.ausport.gov.au (10.x.x.x). Escape character is '^]'. 220 smtp.ausport.gov.au ESMTP QUIT 221 Bye Connection closed by foreign host.

• smtp accepting only for localhost - smtp = yellow, !smtp = red, smtp:s =yellow, !smtp:s =red

$ nc -v windows 25 </dev/null windows.ausport.gov.au [10.x.x.x] 25 (smtp) open $ telnet windows 25 Trying 10.x.x.x... Connected to windows.ausport.gov.au (10.x.x.x). Escape character is '^]'. Connection closed by foreign host.

Thanks, David.

-- David Baldwin - IT Unit Australian Sports Commission www.ausport.gov.au Tel 02 62147830 Fax 02 62141830 PO Box 176 Belconnen ACT 2616 david.baldwin at ausport.gov.au Leverrier Street Bruce ACT 2617

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