I know that there is the TLS certificate file missing. I'm plainly not
sure whether it is missing on my system or on the system the mail is
sent to. I suspect it's the other system since other known messages in
this format always tell an error on the other side, but I'm plainly
not sure about that...
Could someone please tell me for sure that it's the other system? ;-)
dig -t mx otherdomain.de to find the MX.
telnet MX 25
Connected to MX.
Escape character is '^]'.
220 otherdomain.de ESMTP
STARTTLS <-- issue this command
220 Ok <-- if this is the response then you're ok.
If it says "454 TLS missing certificate" instead of the 220 response then
it's a problem with their server. Lately I've been getting a lot of these, I
check the whois, call the SA and they take care of it. Lots of people are
running servers advertising TLS without a certificate.