[Xymon] smtp test - how/what does it actually do?

[Jeremy Laidman]

Ian

On Thu, 28 Oct 2021 at 23:08, Ian Diddams via Xymon <xymon at xymon.com> wrote:

>
> we ahve a client configured thus
>
> 10.108.249.162  colt # ssh ntp MAINTNC:linux smtp
>
> This smtp c
> heck has been green for ever - literally. It has suddenly alerted
> overnight and is remaining so
>
>
> Service smtp on colt is not OK : Service listening but unavailable
> (connect timeout)
> Seconds: 0.001814000
>
>
"listening" means it's accepting TCP connections.


> I can telnet from the xymon server on port 25 fine.
>

"connect timeout" means xymonnet was waiting for something that didn't come
in time. I wonder if you have an "expect" string in the [smtp] section of
protocols.cfg, causing xymonnet to wait for a string containing "220" but
that never arrives.

postfix services on colt are working seemingly correctly  (eg i can send a
> mail successfully from a client that uses colt as a smtp server)
>
> So Im now trying to find out what it is that this smtp check atually does
> in order to find out why it now thinks it cant do it.
>
> The error suggests indeed its a timeout issue - but the telnet test
> connects immeditaely (no obvious lag anyway)
>
> thoughts/
>
> ian
>

Maybe check your Postfix logs to see if something is happening there. Have
you upgraded/reconfigured Postfix recently? In some configurations, Postfix
has been known to reject "pipelining" which is sending multiple commands
(eg "mail" and then "quit") without waiting for a response after each
command. When this happens, Postfix rejects the command, but doesn't send a
"220" nor does it close the connection. Or it might be as simple as your
Xymon server being removed from Postfix's allowed senders lists.

Here's the [smtp] section from the standard protocols.cfg:

[smtp]
   send "mail\r\nquit\r\n"
   expect "220"
   options banner
   port 25

Compare with yours.

You could do a packet capture to see what the dialog looks like, and
compare it to the send/expect in protocols.cfg. You could try simulating
the "send" string from protocols.cfg (after telnetting to port 25) and see
if you get a 220 response. You could comment out the expect string in
protocols.cfg and see if it starts working. You could take a look at (and
perhaps even share here) the banner displayed in the smtp check status
page, as that might give a clue as to what's not right.

I seem to recall a discussion about SMTP pipelining on this list, only a
few weeks ago. Perhaps re-read that discussion to see if there are any
nuggets of wisdom that could help.

Cheers
Jeremy
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