I use the virtual appliance from checkmk v2 (2.0.0p15 (CME)) and I am trying to configure an active smtp check with starttls on port 25.
When I do so I get a warning: TLS not supported by server
But I know that it works because: openssl s_client -starttls smtp -connect $my.fqdn.com:25
works just fine.
I can’t reproduce this.
I have two active checks configured, both with STARTTLS, both working.
Your error says something else, but let me ask you anyways: Are your certificates presented global-signed or self-signed? Is the certificate chain complete?
I found the solution. I had to set the FQDN. Our mail-server forbids a helo like “HELO cm”, thus it failed. With the normal check there is just a 550 and it works. But with STARTTLS it kind of fails silently.
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