It is unlikely that many servers are strong enough to resist penetration and theft of the mail server's private key. That key then can be indexed and matched as

It is unlikely that many servers are strong enough to resist penetration and theft of the mail server's private key. That key then can be indexed and matched as well. Is your mail server refusing downgrades to non-PFS ciphers? Is your kernel not affected by zero-days leaking the state of your secure random pool? Are there vulnerabilities in openssl we don't know about but collection agencies do? Is the reason that the government hasn't announced the CNSA Suite yet because the NSA is busy taking advantage of EC weaknesses combined with quantum computing capability? To say nothing of various direct TLS attacks, which are easy enough to translate from HTTP to SMTP, are agencies putting these to work? How far does the integration of passive collection and active attack go these days - there's plenty of evidence to indicate they have been significantly combined in the past. To say there is no evidence that anyone can break a TLS session is a bit like denying climate change.