SMTP checks

[Ian Diddams]

xymon server 4.3.28, centos 7.9
mail server centos 6 (about to be replaced anyway)

I'm in a bit of a quandary...
we have an smtp check of a server ("oscar").

Literally for "years" (3+) the xymon in house smtp check has been more than happy.

Then since Sept 11th [1] its been flipping constantly beyween green and happy to red 
eg
Service listening but unavailable (connect timeout)


Seconds: 0.001842000
But if I run a telnet test from the xymon server itself it always connects immediately, and responds instantaneously.

eg

$ telnet oscar 25
Trying <redacted>...Connected to oscar.
Escape character is '^]'.
220 a.b.co.uk ESMTP Postfix
mail
501 5.5.4 Syntax: MAIL FROM:<address>
quit
221 2.0.0 Bye
Connection closed by foreign host.
$



All xymon logs show are emails being sent because of the alerts, ad falling statuses that are a result of the constant flipping from red to green. maillog has nothing untoward, ditto messages.

Anyone any ideas what on earth is suddenly occurring that may explain this recent timeout issue?  any expereince of similar?
didds



[1] no changes made around that time etc.  Networks confirm nothing shoing in their logs etc.
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